Not a fan of removing the heroic kill requirement from the Glory meta. The glory metas have been a nice reward for heroic raiders in previous tiers when there wasn't a 100% heroic drop mount.
But there is a 100% Heroic drop mount (yes, more than one will drop on 25-player kills). And we'd like to offer those more consistently going forward. I'd say it was a misstep on our part that Heroic Sha of Fear and Heroic Lei Shen did not offer one.
The "Glory of the ____ Raider" achievements honestly have not made much sense or worked out particularly well for quite a while now. That structure was designed in a world with a single difficulty (3.0 Naxxramas), where guilds that had the zone on farm could make things harder and more interesting for themselves as they pursued those supplementary goals for a cosmetic reward.
But nowadays we have Heroic mode, and as I mentioned above, a good number of achievements aren't really compatible with Heroic mode when done at the intended gear level (I'd like to meet the group that did "Like an Arrow to the Face" on Heroic mode during 5.0/5.1). The result is that the people who get Glory of the Raider achievements are a subset of those who finish the entire zone on Heroic while it is relevant. And often those people don't even get the achievement during that tier. Guilds will either take a week off from Heroic clearing after completing the zone and do an achievement run (often to the chagrin of raid members who don't particularly care about achievement points or mounts and would much rather have a chance at a Heroic Thunderforged weapon upgrade), or wait until the next tier entirely, and then go back with a smaller group and get the achievements on Normal. That really isn't what the "Glory of the Raider" achievements were intended to be.
Without the need to worry at all about even the pretense of making them fair or completable on Heroic mode, we can also make sure that the achievements generally require a certain baseline level of execution (a la "Show Me Your Moves!" or "The Mind-Killer") that will keep them feeling challenging and rewarding. The original Wrath of the Lich King 5-player dungeons were not terribly challenging, yet many of the original Glory of the Hero achievements certainly were in their time.