Even where two skills are clones of each other—and I'm not saying that's okay—I'd much rather have Shadowskin on my edgy DRK job than Rampart, and would rather not have it on my Paladin, merely in terms of name and appearance. Moreover, moving it to a broad "tank" skill does nothing for customization or button-bloat. It'd still be a required choice; you'd just no longer have aesthetic fitting for your particular job, nor the ability to increase or decrease its strength in order to better shape its proportionate value against your other job skills and would remove yet another axis of balancing, in turn forcing those other job skills to be even more like one another. That is not a good kind of "simplification".
Making a universal enmity combo does not save space. It replaces three more unique slots with 3 absolutely homogenized ones that force the remaining skills to then also be more homogenized. It tears apart each tank's previous rotational priorities, where they previously all varied immensely. I don't understand why you would think that would be, in any way, a good thing.
If something tends to remove, remove, remove, with seemingly no intent of adding something in its place... it usually adds nothing in its place.
And why would you want this? Why would you want a job with shield-dependent skills like Bulwark and Shelltron and "Shield" Lob and "Shield" Bash to take on a Greatsword? Do you really think SE would be willing to create new, fitting animations, let alone names or effects, for each of those modified skills, after they'd apparently just removed all variance among (near-) identical skills?
There's probably a good reason Flash was never originally designed to be an AoE filler. Originally, Gladiator had physical AoEs, same as Marauder, and these remained, distinct, even after the removal of most cross-class skills in 1.18. (Flash was merely a ranged enmity nuke, cross-classable.)
Would it really be so wrong for Gladiator to take up a physical, TP-based AoE, such as Circle Slash or Brandish, whether be that be with some unique component?