I've argued in the past that pre-3 players should be given 3 point shooting abilities comparable to players in the early 3 era, say the ABA years and the NBA from the 80's, rather than comparable to all players who actually shot 3's, many of which are 3 point specialists or relentless 3 ball gunners in more recent years. These older players need to be given the ability to shoot threes, but that never should be a big part of their game since it wasn't in reality.
Of course, under the current system, if the older players don't shoot 3's frequently, they are at a further disadvantage to newer players since defenses can pack it in against them. To some degree, I'm fine with that since it feels realistic. On the other hand, I think the current system probably over benefits 3 shooters. Most threes are shot when the player is open. Weaker defense on the perimeter should mean more threes taken, but it shouldn't improve the odds of making those shots significantly. The same wouldn't necessarily apply for paint players, since shots from the paint are almost always contested (except for some fast break shots). Thus, I would think weaker interior defense would result in more paint shots at a slightly better percentage.
How does either situation affect midrange shooters by the way? It would seem heavy paint defense might make it easier to get open midrange shots, but that most of the time, a player would be able to help to challenge the shot itself at normal levels. Again, probably a relative increase in midrange shots without a great difference in the percentage of made shots. On the other hand, a heavy perimeter defense would seem likely to result in similar numbers of midrange shots as normal since the man would still be on that player. However, the help defense would be either further away or more reluctant to leave the post, making it slightly easier to make the shot when it is taken. (I envision a player getting past his defender on the perimeter and pulling up for the midrange shot before getting into the paint. Getting into position to take the shot is just as difficult as normal, but taking the shot should be easier without significant help defense.)
Under this theory, everyone shoots normally at balanced defense. For each move toward paint defense, there is a relative increase in shots allowed by perimeter and midrange players (with perhaps perimeter players increasing their shots at a slightly faster rate) and a relative decrease in the percentage of paint shots made. For each move toward perimeter defense, there is a relative increase in shots allowed by paint players (all at the expense of perimeter players) and a relative increase in the percentage of midrange and paint shots made.