Straight-forward vs needlessly complex. The prevalence of K.I.S.S. (Keep It Simple, Stupid) removes any doubt of which would be more popular.
You cite an incorrect example, which goes beyond simplification. People liked NIN tanks because they took no damage. No damage = less MP spent curing them = faster kills due to less resting = more EXP/hour.This debate reminds me way too much of Ninja Vs Pld in 11, and sounds like people just do not want to tank with a classic tank. I know a bit of over-simplification, but, this is an MMO, people are always going to push for the highest numbers, and, well, SE will never intentionally make a tank job that simply holds hate against everything everyone throws at a mob.
Tanking with a classic tank can work, but the classic tank has to also adapt to what the modern MMO design calls for. You can't get away with having a tank that does 20 DPS when you have a tank that can go a better job at holding mobs and does 70 DPS. This isn't 1997 and we're not playing Everquest. If multi-target Flash could be acquired earlier in the game and War Drum did decent damage, had a good and noticeable enmity spike and was on a shorter cooldown, GLA/PLD would be part of the way to catching up to WAR on multiple mobs.
As I mentioned somewhere else, the main problem comes from the difference in weapon damage and how much it affects damage potential because of it. We wouldn't be having these problems if WAR tanking involved a one-handed axe and a shield. The playing field needs to be levelled between both jobs and any future additions to prevent this current issue from lingering, because at no point should game mechanics ever encourage the community to use one and not the other(s).