I don’t need BiS stats to run the content I care about. Unless you’re high-end raider or M+ pusher, you don’t, either.
Also, again, consider the vault: 2-3 items to choose from every week, compared to a random item currently in BfA. No corruptions, no azerite traits, DRs on secondaries. Higher ilevel will almost always make an item better. It won’t take 6-8 months, more like 2-4 to deck out a char in very decent M+ gear.
That is assuming tier sets will be limited to raids, which they may or may not be, and there’s a fair chance they will not be.
Because lots of people are bad at maths. 
…assuming tier sets will be raid bound. And that they even come back. Blizzard only said they’re considering, they never said they’ll come back, nor that they’ll be raid-bound.
By the second half of the season, where most people will get their +15 achis, covenant choice really won’t matter.
I do know player mentality, I pugged most of my M+ runs in BfA. I got invited to keys on a non-meta spec in S3, and were able to time what I wanted to time. Same in S4 (but it was easier there, because the S4 affix didn’t favour resto druids that much).
I’m also happy to run my own keys, or, dunno, make friends, and run with them.
None of the changes so far made me want to raid. Quite the contrary: M+ seems much more useful to me in SL than it was in BfA. I’m not a high-key pusher, I do not need BiS gear. All I need is good enough gear to do the content I care about, and SL makes that considerably easier for me, without having to step into any raid, at any difficulty.
At the same time, the changes make M+ spamming and heroic split raids for the hardcore 1% much less lucrative, and that’s also a good change. For the average person, these changes don’t really matter, and with the vault, and DR on secondaries, they’re even a net positive.