To the contrary, since barrier scrolls can be used by anyone paladin tends to offer less dmg prevention than other alternatives. Monk is also low on support, but does not need 3 ranks perse.
All clerics should be capable of healing IMO. It’s just incredibly easy for a cleric to have decent levels of healing that has next to no impact on their dmg and dmg prevention. (Chaplains tend to struggle though.)
If you had to take two clerics your team would lose on a good chunk of damage and as such have lower odds of clearing Earth Tower. For up to 20 it can be done however, no idea about post 20.
That and in general your dungeon and grinding teammates will expect you to keep them alive, as they tend to lack healing/defensive skills to do so themselves. (Aside of featherfoot.)
ps. zalciai got nerfed so ignore my statement about spr builds in the post above. It’s no longer true.
And full dex is now recommend for r8 due to the increased crit rate needed for the crit cap.