Regardless of what the developers do, there are going to be people that just try to use their best two guns the whole time, even if they have a bunch of other guns in their inventory. the main problem is people are trying to play the game as if it were Issac, as opposed to realizing this is a different game. I'm very rarely seeing anyone take advantage of the different gun properties. For example, in a room where people might get swarmed by enemies, quick swapping back-and-forth to a gun with high enemy pushback (even if it does low damage) to keep enemies off them. Or if they are at a difficult room, using their best "boss weapon," even though it's not a boss. Or swapping to an explosive weapon (or other bullet nullifying weapon) when too many bullets are coming at you. Or using a piercing weapon (even when it doesn't do very much single-target damage) against a line of enemies. Or using shotgun weapons against groups of enemies. Or quick swapping to damage-over-time weapons for the first attacks. Or saving the disabling (e.g. Transmogrifing/freezing/charm) weapons for difficult enemies (we still have a lot of people that think charmed bow is useless, even though they can charm the big annoying monsters). Or buying the table-tech items, even though a lot of them are decent. Or using the reusable active items as much as they should be. There are a lot of things in the game that people ignore, because they just want everything to be automatic synergies like Issac, that take zero effort beyond memorizing item tables. Combat in Issac is watered down. Your primary damage is generally your tears, which generally don't change unless you pick up a different item. There really isn't much "different things for different situations" going on in Issac. For the sake of comparison, if Gungeon were more like Issac, we wouldn't have multiple guns. Instead, it would mostly be upgrades to your one gun -- even if each upgrade only slightly improved your gun. Most other things would be passives for your gun, which would eventually combine in ridiculous ways automatically. Pretty much everything would happen automatically after you picked it up.

Td;lr it's not Gungeon's fault if Issac players are ignoring game diversity, and then complaining the game doesn't have enough diversity.