I think what you're saying about Whitworth, Sullivan and Saffold is true. Whitworth was the single best position upgrade (going from Robinson) in the entire league in 2017. Sullivan was a steadying influence that was solid yet unspectacular. Saffold went from good to great to LG.
On Havenstein, my view of him is he always had trouble with upper tier, speed EDGE guys. But...
overall in 3 of his first 4 years he was good. Solidly above average in my opinion. Apparently the Rams coaches have confidence he can return to form (or at worst they are willing to have a pretty expensive 6th man).
I think every good OL is greater than the sum of its parts. I'm in the camp that thought Blythe did well at center the final 7 games and is a steadying influence there. And I'm high on Edwards and Evans going into year two. Corbett did better in his 7 starts than I anticipated but I'd rather have him as the 6th man than starting. What's essential is Whitworth not declining further which isn't guaranteed.
I don't expect a top-5 OL. Or top-10. But also don't expect a bottom 5-10 unit either. And really, if they're somewhere in the middle (15th-ish) that just might be good enough.
I also really like Anchrum's long-term potential at RG.
