I been here awhile just like many of you here is what I see.
I see a rehashing of the same dungeon over and over. Terg crypts being one of them. A cleric can easily solo that so can a paladin. There is no way in hell my fighter can and he is even higher level than the clerics/paladins that do. Why is that? Clerics and Paladins get spells that can boost themselves through the roof especially clerics. My fighter would go through tons of potions and still not have the same effect and it being extremely risky. Too risky for him. Must group up. A cleric can practically solo almost the entire server.
One issue to deal with this is to throw more curve balls at them where their spells wont help them. When I played the AMPC, I used a particular nasty long dungeon that a cleric would find it hard to solo because of its size and monsters base there. I forced those players to work in a team by doing that, which was good for them. That is one way to curve a cleric's godhood. Another is having them have a difficult time turning certain undead or affecting certain creatures with their spells because of them not being tied to their god, especially if it is an outlander god such as Selune or Kevelmor. It should help reflect their distance from their god.
Another is trying to rearrange dungeons or areas where a cleric would have a difficult time soloing but if they get at least one other it makes it doable or a hell of a lot easier.
I seen many paladins go up and just kill whatever even if the thing is running away for the xp. I seen so many clerics that just self buff and ignore the rest of the party not even sparing healing for them. There are lots and lots of players like this and I think a good chunk of these players don't read the forums. I even send them tells explaining the distance from the god bit and you get a response from some of them like STFU. Then again I met a lot of good roleplayers and good clerics that stay back, heal, spread their power to others, same goes for wizards, and paladins. Think with clerics or paladins, especially paladins, is to enforce dogma or code of ethics you need a DM to be on their back, but personally I rather have DMs help with glitches, run stories, and help with more unique aspects than policing clerics and paladin PCs.
Also I notice from stories or plots, that even if a DM runs it, players tend to ignore it as soon as the DM is not there or isn't being enforced by a DM. And when you tell them this is what is going on you are being told you are crazy or something like that.
The problem is mindset, and there is only so much you can do to enforce it mechanically.