Starfield is currently a 4-5/10 game and by the time Modders will be done with it, probably a 9/10 game (10/10 if someone mods the whole main story out of the game).
But that's not what modders should be wasting their time on. They shouldn't be fixing the game.
Besides, the changes and oversimplifications Bethesda has made to the engine and the extraordinary announcement that the modkit will take a year to be released, will vastly delay the amount and quality of mods that will be released for the game.
Baldur's Gate was a 7/10 game on release, mostly due to the issues with Act 3. But they took all of a few weeks to fix the vast majority of major issues and bring the game upto 9/10. Every patch and hotfix they released fixed thousands of small and large issues.
Meanwhile Bethesda announced updates right after the game released, fixed like 4 progression breaking bugs and nothing else.
10 days after announcing they were working on bugfixes and patches, not a goddamn peep, not a single thing fixed beyond those 4 small fixes.
It's straight up disgusting how these corporations operate.
All of their games have their mod kits release about that long after the game comes out, so while I can understand the timeline seeming excessive, and I might agree, it's less extraordinary, and more predictably ordinary.
And your 5/10 is my 7/10, so tastes will vary. I think a lot of what makes Starfield problematic is inherent to its design and the growing pain of them moving formats to space and not simply a bug issue, though the bugs are absolutely there, so making your personal rating of it a supposed effect of its bugginess is, I don't think, completely accurate, but your point still stands.
I am waiting for more paid skins to be tossed in the game. I wonder if the mod tools will somehow try and block weapon skins so it stays an only paid feature.