The spiders were made to be sniped. The map rewards patience over daring. It's extremely unlikely to make it over the steps and platforms with them still alive. And even so, if you dilly dally too much on them, the imps below will step onto the teleporter and start applying pressure from the back, at least from sound alone. The pit itself is punishment for failing the platforming, not a place required to visit.
The final fight is a bit weak as more often than not, the barons don't apply too much pressure, which might panic someone back into the pit. Maybe some linedef alignment and repositioning of the enemies could help it. Ideally, the player would feel compelled to walk in and keep firing, taking care of the weaker enemies to make room for dodging the barons' attacks.
The chaingun's up on the pedestal in the first section, where the second set of imps and first cacodemon pop out of. I assumed it was pretty obvious and visible, but maybe I should have added something to it.
Both pits are optional. The first has the super shotty to aid with the knights, but it's not required for the pinkies, as the chaingun I assumed would be acquired should suffice. The pinky corridor itself was made to punish any and all forms of rushing, be it early on to engage the first set, or later after they have been dispatched. Lack of chaingun at this point would indeed render it difficult. Potential lack of ammo has been compensated for with supplies near the lost soul windows.
The second pitfall is more of a punishment for any sort of rushing or mishandling of the platforming. The arachnotrons themselves are there to discourage carelessness from the getgo, having to be sniped, which also gives time for the imps below to step onto the teleporters and warp closeby, which can result in pressure, at least from the player hearing them.
The final fight encourages mobility, unless the enemies bump too much and can be sniped by just backing off. Keeping the trigger pulled and walking in worked best for me when I playtested, requiring careful circling to take care of the barons. Any player who starts pushing the buttons before the barons were killed would be surprised by imps in the dark blocking the way to the switch, though I doubt many would be tempted to skip the last bit of the final battle.
At least these things were my intentions. I apologize for not making the chaingun more obvious, probably would've made the map a lot more fun for you. Last room should also have been built better, to encourage determined play, failure of which would result in retreat and fall.