Sure. Maybe a better comparison would be warlocks vs sorcerers. Warlocks have had issues with multiple stat dependencies, and then along comes sorcerers which are also big damage arcane strikers - and yet, warlocks haven't faded from the game because of this.
I think this is really the biggest flaw in your argument. You look at the Knight and the Shield Fighter, and say, "Only one of these can be the best at the job, and the other one will fade into the background."
But... that's not how the game works. We've got strikers of various power levels. Most tend to agree that a few of them 'come out ahead' of the others in the long run - but the fact that rangers and multiple attacks is really really strong doesn't mean that people only play rangers.
For one thing, the differences aren't enough to overwhelm the game. A ranger and a warlock can both be in the same party and feel like they are both doing a good job, even if the ranger might pump out more damage more often. Similarly, the Knight and the Shield Fighter are both going to get the job done - one isn't going to emerge as 'the only possible sword and board defender you can play.'
Secondly, people have different preferences. Some will find the specific elements the Knight offers more appealing, while others will prefer the PHB Fighter. And both can continue to be supported. You feel only a limited number of feats will apply to both - but look at some of the class articles out there. I can recall a Warlord article (before Martial Power 2 was even out), and the bulk of the feats were tied to the 4 different builds, which meant any given character might only be able to use 1/4 of the article (or slightly more, with the handful of feats for all warlords.)
But that wasn't inherently a problem - not if those feats were still useful.
The Warpriest does have some advantages, in being able to more freely grab the implement wisdom powers of the cleric - which gives them some flexibility, certainly. On the other hand, those expanded options don't particularly help it in its role as a pure melee cleric, so the Str-cleric might still have the edge there. Regardless, it seems extremely unlikely that the appearance of the Warpriest will naturally cause the Str-cleric to just vanish.
After all, I don't see anyone claiming the Runepriest caused that to happen - yet similar logic could be applied there. An entire class focused on a melee-wielding Str-based Divine Leader; shouldn't that have rendered obsolete a single build for the cleric with more limited options?
