It's not just that the focus is on raiding, it's on an incredibly small number of raiders and even then it's very boring without better progression for most of them at the bottom of the ladder. Look at the kill timing from:
https://progstats.io/tier/28-sanctum-of-domination
For most bosses, the number of guilds killing them peaks in October and then drops precipitously. There are maybe 2500 guilds who are gonna kill Sylvanas, which is like 50k players. And after a few months, no one new is even trying to progress into mythic at all.
Now compare this to Dragon Soul. Yes, I know Dragon Soul was a bad raid, but it did one thing right - it got much easier as time went on. Dragon Soul was released in November, and in July (8 months later), there were nearly 2000 guilds who killed Madness for the first time. I literally pugged CE Deathwing just before prepatch and I was a significantly worse player than I am now. It had the zone buff that made it easier and allowed guilds who weren't good enough to progress.
Meanwhile, today, I have a buddy in one of those barely cutting edge guilds (sometimes not, depends raid to raid). They spend about half of each tier on a giant extended lockout, slogging through the raid one boss at a time, hundred attempts on this boss, fifty on that one, etc. If you raid 3 hours a night and wipe every 10 minutes, that's 18 attempts, so a 100 attempt boss is 2 and a half weeks of wiping.
When I think of my best times raiding, I think of going in to a fresh instance, powering through the earlier bosses we mastered, getting a bit more powerful as we go so that the hardest boss is a bit easier each week. That, to me, feels like progression. Doing 40 attempts on a boss and saying, "yes, we got to phase 3!" isn't. And yes, we weren't super hardcore but we progressed every week, and yes, the zone buff helped us significantly because we just aren't as good as the top 20k players that they design the raid for now.
If my buddy's guild gets cutting edge this tier, they'll probably stop raiding. They haven't done some of the fights in months, and they barely beat most of the later bosses.
This is just a worse raid design. They need some sort of self nerfing mechanism for mythic, whether it's a zone buff or whatever, because most people just stop playing the game because the current design doesn't include enough progression for most players.
People here will snarkily say "well that's what heroic is for". Heroic progression takes a month, maybe 6 weeks, then your character is hard stuck unless you join a mythic raiding guild and start slowly slogging through.
So again, Dragon Soul you had significant progression happening 8 months into the raid. SoD's progession is basically non-existent at this point - you had about 100 guilds kill Sylv in the past month, which is 2000 players (and 1/20 the number of guilds killing Deathwing in month 8). This is because they used to significantly nerf content as it went on - with gear, with zone buffs, legendaries, valor upgrading gear, you name it - and now they just leave it as is, designed for the very top mythic guilds who are good enough to clear it every week, while most players just hit their ceiling after 6 weeks or so and give up.