Even in Solasta (which can only use the free license bits of 5e), I am not asking them to 100 % respect the rules : 5e rules are not perfect. But Larian designers should not butcher the rules on a whim without more thought. As far as I know, Larian is the ONLY game studio to have been given the license to use 5e rules (i.e. there is one other studio making an action game using the D&D name, but it does not require 5e rules as such).
To be precise, all of the 5e rules are released under the Open Gaming License that Solasta uses. What Larian has is a license to use WotC-owned and DnD-related IPs and trademarks.