The OP pretty much hits the nail on the head, on one hand we have overly simple raid with alex nm and on the other we have viciously tuned savage. The fights themselves are not incredibly fun or interesting either. Arguably pepsiman was a well done fight, but I don't think I know a single person who's turned around and said "oh boy I love Manipulator so much! Can't wait to go back in there!"
I've noticed the same thing, my linkshells are emptying out, people are quitting, people are leaving server hoping they'll find something better. I personally don't mind the challenge given to us by A3 and A4 but it doesn't take a PhD to see that a lack of a middle ground destroyed a lot of groups motivation.
The mid-core and even lots of hard-core raiders are quitting in droves. A single person quitting your static could spell the end if you can't find a suitable replacement. And lord is it hard to find a suitable replacement, even during coil.
Yaaas, SCoB was easily the most fun raid tier for me. Tuning was perfect imo dps checks and mechanics were well thought out. Groups spent most of their time learning how to deal with mechanics and the fights were tuned so that players outside of the "true elite" (or however we're classing the world first players and such) could still reasonably kill it before nerfs/echo.
Basically it was poor wording. Savage Alexander =/= Savage SCoB simply because savage second coil was completely optional in the sense that it removed 2/3 from the points in the OP. There was no new story (obviously), but there was also no relevant loot so there goes two large motivators for players/groups. The remainder of the people who did it (or desperately tried to find a group to do it like myself) usually did so for the challenge, the fights were mechanically very fun even though they were extremely difficult.
If they dropped alexander normal on us with i190 gear then dropped savage alexander with the exact same gear but just titles you'd probably have the exact same reception that savage second coil got. Massive lack of interest until people were just simply so bored that they'd try it.