I've been getting a lot of mileage out of Hungry Hungry Hadar (Hunger of Hadar) using Wyll; it creates difficult terrain with damage but crucially blocks vision so enemies can't just jump or teleport out of it, unlike Spike Growth which is basically useless in BG3. Combined with Devil's Sight Wyll can then just take up cover and pop out to eldritch blast anything trapped in the area.
But yeah, there's a definite problem with maintaining concentration given the quantity of enemies, and number of enemies even in early areas that have multiple attacks, spells and/or AoE items like arrows or bombs; with War Caster I managed to make eight concentration saves in a row on a character, but that was the exception not the rule, mostly my spells were wasted on the round I cast them, especially if I spent a higher level slot on them.
Because Larian want us to us DOS mechanics for the fights (Potions, explovisv barrels, molotow cocktails ...) they are unwilling to implement D&D battle mechanics and spells properly because they are unable to break with their beloved DOS.
