This is a massive overstatement. It may not have as high a DPS potential as the other healers, and the Lily system is obviously in need of a major rework, but I don't feel it's ridiculous at all. If it was that bad, nobody would play it in Savage raiding, and yet plenty of people do. And it can even solo heal everything as well, as far as I know, with the possible exception of some raids that absolutely require shields. Although some of those can be covered by tanks.
And it has a playstyle that is really rather enjoyable. Cure III, Thin Air, Asylum, and Plenary Indulgence are very satisfying skills to use. In comparison to Earthly Star and Collective Unconscious, they do have some drawbacks, but also some advantages. The advantage of Cure III is that it doesn't have a cooldown, and doesn't need 10s to reach maximum potency. The advantage of Asylum is that it has a longer base duration than Collective Unconscious' regen, the latter of which can be extended, but does so at the cost of a 120s CD ability. Asylum could use a small potency buff, perhaps, and/or a radius buff.
But ultimately, WHM is the most satisfying healer to play from a positional point of view. AST and SCH are frankly allowed to take the lazy route to positioning. Party members have a lot of freedom to move, and still get healed. With WHM, that's not the case. You can call this a massive flaw, but I look at AST and SCH and think it's boring that you can skip so much positional optimization. I mean, hell, if we're busy talking about how WHM is "bad" because in top tier parties, it can't output as much DPS, and it's healing tools are "weak", the topic of it's hard-to-use abilities really shouldn't come up, considering it's a "top tier" party that should know how to work with a WHM, and yet it does. Just because it requires more party coordination doesn't mean it's bad. Some potencies could use a buff, a shorter Stone cast time would be nice, and the Lily system needs it's rework, but I have no issue with WHM's current position. Least of all its identity. Because it does have an identity. It's the game's compiling healer. Though actually, the buff to Plenary Indulgence hurt that identity a bit.