the SF skills is the key thing that shifts in the team composition from the 2-3 to the 3-2, although i do agree the 2nd biggest thing is the center.
all 5 players in zone contribute to the defense of every shot. the contribution of each player depends on really 2 factors, one being their position (in the 2-3 or 3-2), and two being the distance from the basket, of the shot.
in a 2-3, the 3 is being calculated on a SF/PF formula that basically favors forwards, so ath over speed, with significant but not huge value on blocking. a true SG playing the 3 is basically going to contribute poorly in that scenario. under a 3-2, the 3 is being calculated on a PG/SG/SF formula that favors speed over blocking and with a bit less emphasis on ath (ath is important to defense in all circumstances in all systems). a SG is going to do well defensively in the 3-2.
on the C front, in the 2-3, there's a PG-SG formula, a SF-PF formula, and a C formula. so while the C doesn't stand alone persay, its fine to think that way, and the C does get his defensive contributions calculated uniquely. that calculation turns heavily on block, more so than for any other situation in HD. because the block matters more, and because ath, def, reb are all very valuable, it is relatively normal to take your LP scoring at the 4. however, its also normal especially in d1 to just have a superior big, and to play him at the 5 and to get your scoring from there. either way is 100% fine.
anyway, all that said, i REALLY like to recruit good SFs in zone. i think there's substantial value being able to switch from the 3-2 to the 2-3. you always *can*, if its REALLY called for. i would run a 2-3 against a 0% 3pt team no matter my SF, most likely. but i really like to have the flexibility where i have a SF who is one of my better, more versatile players, particularly on defense. most of the time, if your SF has nice ath and speed, hes going to be strong all around, but not always. so i guess i'll say, a versatile defender at the 3 is the goal, but its just sort of natural that if you prioritize ath/spd both at the 3 and prioritize recruiting resources towards getting a strong 2-3 and 3-2 sf... that he'll end up being a strong scorer and stuff, too. i love those guys and the flexibility they bring! ath is much more important than speed for such players, not sure your division but a 95 ath/def 65 speed SF can be legend in high d1, while the reverse (65 ath, 95 speed, 95 defense), definitely is not.