This is how I look at things re: PoE's system and systems in general.
IMO, PoE's system can be described as essentially a 3E/4E D&D hybrid plus Sawyer tweaks.
First, I think PoE's solid foundations in RPG design have gone under-recognized. People look at it and see a horrendous mutilation of the AD&D they remember from Baldur's Gate, rather than a game that follows many of the same steps that WotC themselves did in the 2000s. It's easy to see why - we never got a proper tactical RTwP 3rd or 4th Edition D&D game in the 2000s (IWD2 was an easily ignored, partially implemented black sheep of a game, and NWN2's combat was a joke). There's no really good frame of reference for properly evaluating what Sawyer did with his systems design tweaks.
If the difference would have been negligible with any other modern incarnation of existing RPG systems doesn't that play into what people are saying that all the time Sawyer/Obsidian spent creating their own systems is essentially wasted? They could have gone with something established and allocated resources elsewhere.
For all Sawyer supposed system design excellence (that is supposed to be his forte, along with understanding the importance of history when designing settings), you say his work in that aspect of the game had no noticeable impact (no more than your average house ruled D&D).
But, more to the point of this discussion, I think systems are moderately important to an RPG's quality. I think they're especially important for replayability. You play the game once, you're mostly thinking about the content. Play it again, now you're looking more at how you can tweak your experience via the systems. But that's looking at the system as a whole. As I said, PoE's system isn't just Sawyer tweaks. It's that D&D foundation PLUS the tweaks. The tweaks alone, IMO, just don't really matter that much. They're quality-of-life stuff that people have obsessed about to a disproportionate degree.
Then it depends on how much stock you put on replayability, IMO it is (or should be) one of the key strengths that separates RPGs from other genres. Of course even then systems are married to content, if encounter design is lackluster for example it takes a lot of fun out of trying different classes, party compositions, items etc.