You have absolutley no evidence for thinking that this company "were in way over their head" or in over their head to any extent.
It's an educated guess. Baldur's Gate 3 is a first for Larian in multiple ways. One of them is the Mac port was released simultaneously with the PC version. Previous games they worked on had the Mac port released long after the PC version. Like with Divinity Original Sin 2, the Mac port came out in 2019, 2 years after the PC version and 1 year after the Definitive version. So they were just porting a finished game to Mac as opposed to continuously updating a game over the course of several months and maintaining parity with the PC version. That tells me the studio is over their head.
I'll bet you couldn't even name the company.
It's a Russian studio named Elverils LLC. It's even on their website.
https://www.elverils.com/Six months after release and we have the 6th major patch and its still huge yet people are still praising Larian for fixing things which should not have been broken in the first place.
I'm not praising Larian for this I personally think they should've waited to release BG3's various ports until after its updates are finished. It's clear DOS2 benefitted from this approach by comparison. I personally believe this also contributed to the toolset's delay which is more infuriating than anything else tbh.