In my understanding, these spells are working this way because of the overpower they can cause within the game, so a certain difficulty was created to cast them in order to balance these abilities.
I doubt it. First of all, concentration based spells in BG3 are already difficult to hold on to, due to the multitude of sources of guaranteed damage. For example, if I try to cast bless or bane when fighting goblins they will start chalking unavoidable granade and more likely than not will get the spell cancelled before I get any value out of it.
Also it is still very possible to target all the characters you want - the AoE previews selected targets, so it is just a matter of being patient and wiggling it around, until AI picks units you want. It does what you want it to do, just in a very inefficient and frustrating way.
