People aren't only quitting Savage because it's too hard. They're also quitting Savage because there is not enough incentive to grind through progression. No new story, no new fights -- just new mechanics, no new gear -- just recolored NM gear. If there were more rewards, then more people would be willing to tough it out.
If you think that the top raiders didn't complain about the difficulty of the content during progression, you weren't paying attention. Their twitters were littered with complaints. The difference is for top-progression raiders, the pursuit and the clear is enough to motivate them. For mid-core raiders, there needs to be more since they don't care about being top 10 in the world, server 1st, or part of the 1%.
As for the two being night and day, they're obviously different in ways. But, you are getting caught up on details rather than understanding the actual point. To experience anything in this game, you need to invest something.
To experience the entirety of the classes / jobs, you need to invest a lot of time and possibly a lot of gil to grind it out.
To experience the entirely of the raiding content, you need to invest a lot of time and possibly a lot of gil but in different ways. That time goes into research, learning and grinding of a different sort. That time also goes into networking.
Some people are okay with the grind required for classes / jobs. Personally, I would rather quit this game than grind fates / dungeons for weeks upon weeks. I don't complain that they need to make the leveling experience better because I personally can't deal with it.
Some people are okay with really learning how to play their role and learning the content. They're okay with the networking required to find raiding mates. Coil with echo + over gearing was not that hard to clear through PF and I knew plenty of very mediocre players that still cleared T13 with some effort.
You can make the argument that one requires more effort than the other. That doesn't matter. Should everything in this game be low effort? Should people be entitled to experience everything with no significant investment?