Yeah, I am willing to go with the mechanics feeling clunkier because it is still EA and some copying of the DOS engine may not have gone flawlessly. But that does still make it feel like a Tech Demo. It works, but barely. With a focus on the writing/origin characters.
I do not doubt Larian understands 5e rules. It would be silly to assume they did not research. There are oversights with the houserules/adjustments/homebrew they used in the translation from 5e to CRPG that seem maybe minor but ultimately have a huge effect on how some classes play, how it makes some spells/abilities pointless and generally the feel for the game.
Random encounters are one of those things that is more related to worldbuilding/storytelling in my opinion (It is an event, basically) where something like reactions is a (in my opinion) large part of the rules. Many classabilities and spells are made to function around reactions, afterall.
As it stands it all comes across as an initial copy paste of the DOS systems, and then reskinning it with the 5e ruleset rather than make a system based around the 5e ruleset, and then fiddle/adjust with houserules based on feedback/testing. For me, someone who was hoping for a 5e CRPG experience (That was the a sales pitch, afterall. Aside from brand recognition of Baldur's Gate, but that is a different subject and not related to 5e core rules) this raises quite some concerns still.