Is it really? How contested do you really believe that Emberflow would be if you could buy those tomes from a vendor? Do more people kill MK for Hellcall or the Dodging tome?
Pretty sure the answers to those questions are: no, lightly, and the tome.
I completely understand having nothing to put yellow numbers in and feeling like there's nothing left to do in this game. A month ago, I was there: in an inactive guild, farming my supreme, actively trying not to gain experience points while doing it because I would run out of books. I just think that some alternative path to put experience points in is a better long term answer than opening up the raid tomes to everyone.
Making these tomes raid-only seemed to be a way to slow down your XP progress by something other than how fast you can accumulate yellow numbers. With that mechanic gone, people will progress to being done with all relevant opus 2 tomes while still raiding ToT, Frost, and ED maps (speaking nothing of the balancing impact that would have on the content). Then they'll retire with nothing to XP, just at a different number of books on fomelo.
tldr: just saying that giving existing books to more people does not solve this problem, only pushes it down the road a number of months.