Don't get me wrong, I dislike that rule as well - then again I kinda dislike the whole action vs bonus action 5E f**kery (or 4E minor actions, but 4E had even bigger issues). While it makes perfect sense from a rules/balance perspective to not allow the conversion of bonus actions to actions, it makes no sense from the perspective of "realism" / suspension of disbelief. Realistically, a character SHOULD be able to do two bonus actions (and no action) per turn if they can do action and a bonus action per turn, as bonus action is supposed to be easier/shorter. If jump is a BA like in BG3, then jumping twice per turn (6s) and taking no action should definitely be possible if jumping once AND CASTING A SPELL is OK. And balance in BG3 is a moot point, the whole game will have to be rebalanced, Larian's implementation is simply not D&D 5E and spells, abilities, classes etc. will have to reflect that.
That being said, the combination of Misty Step + specific offensive spells is definitely very powerful, if not OP. Use all movement to move in the middle of enemy group, cast Arms of Hadar or similar spell, misty step away (used and abused in BG3). Whether it is OP or not really depends, are there any actions that are not spells, but have a similar effect? Andi f yes, what is their "price", do they expend an item/slot/charge or something?
Interesting thread:
https://www.enworld.org/threads/removing-the-bonus-action-analysis.554034/I generally like 5E TT for its simplicity, though I think 3/3.5 is by far the best ruleset for CRPGs. Taking 5E, removing the spellcasting rule, allowing to use BAs as As and rebalancing accordingly would, IMHO, lead to a perfect and simple ruleset for P&P.
