Man during WOD I was in a 2 day raiding guild, rank 2 in the world for 2 days progression, time well spent on focused raiding. On Legion launch I played in a guild in the top 100 progression, and yes the time commitment was much higher in Legion, but still only 3 raiding days.. Legion required more grinding and time commitment to raid than TBC by a long way, it's not even comparable.
The difference is what you spend your time on. a 1x realm requires you to set aside a massive amount of time doing what is essentially meaningless grind, it has no impact or provides no benefit to the preparation or process of your goals of raiding or otherwise, it's simply a prerequisite to start, so from my point of view the less time I waste on levelling up the better.
TBC doesn't actually require a hardcore level of playing to be able to maintain solid raid progression, I raided 3 nights during retail TBC for 3 hours per and the only bosses I did not kill pre 3.0 were Muru and Kil'jaeden. Once your char is capped 70 and setup in TBC the actual commitment required is quite low, unless you're going for server firsts, which is such a minority group to begin with.