I have yet to not take an AOE skill if a monster has one. However, I am wondering, do I need to do that with every monster? I think there is some benefit in maybe have all single enemy skills and loading this monster up with two strength and one speed rune to make them a hard hitter. Has anyone taken this approach and if so with what monster?

I have with some because I already had others in their elements/books with similar or better aoes (special damage or with an added effect for example) and these monsters have solid single attacks like it hard hitting, zero cooldown or decent effects such as arcade with 2x stun and 2x stamina drain.

Others (2 strength 1 speed rune monsters) I've forgone aoes on are osteoclast, lau lau, greedy dragon and terroriser. Maybe some others I can't think of right now. Situational for team wars but I've learned having such a setup can sometimes lead to a safer victory. I also kinda dislike the lowered accuracy on aoes.

Hirondelor works well with no AOE skills even though he has good ones available.

I always check the recommendations and check with my own idea of a monster often they come up with the same attacks but I always take my gut feeling about it

There is no a general approach like either take the aoe or leave them
it all depend on the skills and the state effects they have , and in most case you can take both

For example General atum his highest 60 point attack " atum mace " is a must have and it is even 0 CD so you can take " earth offensive " as aoe stun denial move and maybe" Armored troops" as a support one

Area Controls (Crowd Control) skills are almost mandatory (Stun, Freeze, possession...). Also area buffs or heals to our team.
I like area damage with torture effects (Damage over Time) because they have a potential very high damage (on the hit and after), but some times