I think the idea behind Acid Splash taking away AC is that it's corrosive. There are ooze monsters in 5e that eat away at AC in a similar fashion. The problem is, it's a pretty hardcore ability for a cantrip that doesn't cost a spell slot.
I can see the logic that Larian is using, but I think spellcasters might outpace martial classes if the extra cantrip effects remain.
