Savage does not unlock at the same time Ultimate drops. The devs tend to unlock it about 4~6 weeks prior to the next tier. But they most certainly do not unlock Savage at the same time as Ultimate releases. UCoB released in 4.11 (2017.10.24). Savage was not unlocked until Patch 4.18 (2017.12.11)—Patch 4.2 was 2018.01.29. UwU dropped in 4.31 (2018.06.05). Sigmascape was unlocked in 4.36 (2018.08.07). TEA dropped in 5.11 (2019.11.12), and Eden’s Gate was unlocked in 5.18 (2019.12.24).
All jobs require a mixture of tome and Savage gear. If you are clearing a tier early, then you will have more than enough time to start getting gear on other jobs “while the content is still hot”—especially in a static setting where groups determine alt/secondary jobs for members and hand out freeroll drops based on that (I’ve had BiS on DNC for a few weeks now, and I was already gearing healers since all I lacked was weapon and body piece for DNC—and I actually didn’t clear this tier as fast as I have cleared in the past). The tiers are relevant for 2 patches anyways, and outside of Ultimate, nothing is harder. There’s plenty of time. Eden’s Promise is going to remain relevant up until 6.0, because people will keep venturing into it during the lull that occurs post-5.5 leading up to the new expansion do learning parties, farms, parse runs, etc..
Be glad they unlock it at all, to be honest. Before Stormblood, the developers didn’t unlock the tiers until the next one released (with the exception of the final one, which would unlock about 1~2 months before expansion drop).
Honestly, the only book requirement that could stand to be reduced is the belt. Why is a belt 6 books instead of 4, when it’s not nearly as good as the other 6-book pieces (head, hands, feet) or prioritized over any of those unless you are trying to reach a stat tier (which is min-maxing at that point, and not something every raider really does). Offering exchanges of higher-tier books for lower-tier ones is something I’ve also seen suggested in the past that I would not be against (e.g., you can trade E11S books for E10S or E9S books—especially helpful if your job is one of those this tier that requires all 4 Savage accessories). However, I don’t see the issue with weapon, body, and legs remaining 8 books. The Savage weapon will almost always be the best one you can get during a tier (with a few exceptions—current tier BLM weapon, Alphascape MCH weapon), so it should cost a decent number of books.