its a good question. i've never been fully satisfied with my own thinking on the subject. along with help defense, you could also throw in defensive switches - one would think it makes little sense for a man defender to contribute 100% of the defense for his assigned guy, when things like pick and rolls and help defense pretty clearly exist. but this game does often lack depth and nuance in areas we logically assume it has it - so we kind of have to be careful in taking that line of thinking too far. one of the things that i think helped me in learning HD is that in the early days, i included next to zero basketball know-how in my assessment of anything (partly because i lacked it, partly because the numbers side is so much more intuitive to me). this was always a simulation/math game with some basketball window dressing, to me.
i wouldn't say blocking should be ignored in any system, today, but i've definitely talked about how i personally ignored block more or less entirely in my early d2 pressing days, on a number of occasions. but i also said... i essentially ignored blocking, speed, perimeter, ball handling, passing, free throw, and durability in my bigs. while that was all pretty true, and while the program in question was one of the ultra-successful ones, that doesn't tell the full story.
there's a few things i would add to color the situation more appropriately. first off, and most importantly - i was a new coach, and like all (smart) new players in any game, i focused on what mattered most. i figured once i was on top of those things, i'd move to the next layer out, and so forth. i ignored things that mattered, because i could only initially tell what REALLY mattered, and that is where i focused. i ignored a lot of things in my bigs that i absolutely do not ignore today. also, two other main coloring factors. one is that the game was fundamentally much different. press was overpowered in ways it no longer is, and guard offense was overpowered in ways it no longer is. conventional min-maxing will lead one such as myself to sell out fully for those out-of-balance items, and i absolutely did so. i basically barely used big man scoring (per and spd both matter a bunch). i also ran triangle which turns more on big lp than other sets. all i wanted from my very-low-distro bigs was rebounding, and to a lesser extent, defense (i was fine with opposing bigs scoring, as big man offense was strictly inferior in those days). also, this was a long time ago, the quality of coaching in terms of team building and in terms of actual coaching, was generally much lower than today. i didn't have to have the best team to be a major favorite. so i could be wrong about quite a lot - and i was - without it really costing me much.
the other big difference is, then d2 with the lower talent levels of old d2 (compared to today's d2) is just way different than high d1. i basically stopped ignoring speed and per in high d1 from the get-go, even before *any* of the 2.0 changes (which came in stages over about 2 years) hit. high d1 is a lot different because offense and defense are in balance. offense has *always* had the upper hand in lower talent levels, because you'll still find pretty effective scoring ratings on the top scorers at those levels, which generally speaking, defensive ratings can't hope to match. its way easier to get a 90 speed/per guard in today's d2 than a 90 ath/def guard, its not even close, right? anyway, in d2 where offense was ascendant, and in a time when guard offense and press were essentially broken, it was pretty appropriate to recruit bigs purely on their ath, reb, def, and sta. but today's game is much more balanced, and high d1 has always been much more balanced offense/defense wise. one last thing - recruit gen is totally different today. reb, my #1 rating from that era, was very tightly linked to height, as was blk - so the reb/blk correlation was massive. i didn't have to care about blk. by caring about reb, i got plenty of blk.
anyway, back to the original question, i just wanted to color a bit, why i don't basically um... disavow my old strategy, if you will. i think it was highly appropriate in that day at that level, for me to essentially run my front court off 4 key ratings (reb, ath, def, sta). it wasn't a perfect strategy, but it was better than basically any one else's. but anyway. i have looked a bunch of times for help defense, defensive switching from pick and rolls, or whatever else. i just don't think there is much of it. its always hard to tell was is a small factor versus a non factor. a good analogue is speed in rebounding. most of us assumed speed was a small factor in rebounding, because it made sense. admins have stated unambiguously that it isn't, and we basically all accept that. personally, i was highly surprised - even though i had just spent two years ignoring speed almost entirely in bigs and had all time great level success doing so. we have to be *very* careful about imposing basketball logic on this game. basketball logic informs our thinking, but we have to pay ultimate credence to the results we actually see on the court (which is tricky because they are very muddled, very obfuscated).
my take is that even though it makes no sense for a man defender to contribute 100% of the defense to the opposing player, that it is very possible that is what is happening. i do definitely allow, in my thinking, for man defense to essentially be 80% the key defender, and 20% the team. that very well may be. but there is essentially no chance in my understanding, for the opposing defender in m2m to contribute less than a substantial majority of the defense. help defense, defense switching... i can't say they don't exist. its extremely hard to distinguish with the naked eye, between small and non factors. but at best, help defense, defense switching are small factors.
press is very man-like. so the same applies to it as man, more or less - at least in this regard. block is just not that important in man or press. in press especially, for two reasons. one, because press relies more heavily on phase 1 of defense, the prior-to-halfcourt phase, where block is 100% useless (or very close). second, in press there is and always has been much more going on, there's just more that matters between depth and stamina and turnover generation - so anything that is not of increased importance in press, is therefore, of decreased importance. plus, guard-like 3s make more sense in press, which emphasizes the need for reb in the bigs, which indirectly reduces the importance of everything else, for bigs.
zone is different, but its not help defense, its not defense switching. in zone, all 5 players contribute to the defense of every shot. they are essentially all averaged together every play, although there is a distinguishing based on shot distance from the basket, which presumably allows for the emphasis of different ratings at different ranges. i would say, all 5 players are averaged for every shot. i would not say, all 5 players are equally important in the defense of every shot. anyway, the equations for how much a 3, 4, 5 contribute individually in zone, turn much more on block than man or press.
its possible that in man, 20% or so of the defense could be help defense, and in press, this could be gone, because the help is busy doubling for turnovers. this might explain part of why blocking is a bit more important in man than press, but i think the other two reasons (press valuing the full court phase more, and just having more going on in general) explain enough of it. i definitely cannot rule out that in man, what you are theorizing, is happening. its just a small-ish factor at best.