I would make the argument using armor comparisons in GW1. During Prophecies, the earliest you could get max stat armor was at Droknar's Forge, which was supposed to be relatively end-game content. Imagine that after Lions Arch, after basically half the game, there were no more armor crafters. You had to go through Maguuma and the desert using only what was available from LA. Would it be hard? Yes, but that's the same boat everyone would be in. Now, lets say that in a patch, Anet added a crafter to the Henge of Denravi who made gear that was in between the stats for LA and Droknar's. Is it better for those who haven't yet reached Droknars? Yes. Is it as good as the best available? No. Does getting the Henge armor get you any close to Droknar's armor? Nope. Does getting it give you another short term goal, and something else to do while you progress towards Droknar's? Yep.
This is a totally different hypothetical scenario than what is happening with GW2. You're describing the addition of a vendor that sells gear that is below the current best-in-slot in order to bridge a gap between best-in-slot gear and something lower witihn a game that's designed such that you don't need specfic gear to complete content. Ascended gear is better than the current best-in-slot, exclusively is able to hold upgrades that are necessary for completing certain content, and "bridges the gap" between the previous best-in-slot gear and a prestigous best-in-slot gear by itself being a new best-in-slot gear.
If you wanted to make a GW analogy, it would be like the developers adding a third god realm of several levels with deeper levels containing enemies that applied a new type of Spectral Agony which could only be protected against by upgrading a newly introduced set of gear that universally has better stats than what was previously the best. This analogy doesn't have the new gear acting as a bridge to anything, but nothing in GW was designed like the legendaries of GW2.
At no point in GW1 or GW2 did you need to have the best gear to enjoy content. Did it make life simpler? Sure it did. Were you prevented from playing the rest of the game if you didn't have the best of the best?
As of the moment that Agony is introduced to the game, yes. The new dungeons will eventually put players against stacks of Agony that can't be overcome without the use of ascended gear, and thus you need ascended gear in order to play that content, which means you need ascended gear in order to play all of the content in the game. If instead they don't throw sufficient Agony into the new dungeon to require players to move up to ascended armor, then what was the point with adding it whatsoever? It doesn't serve as a bridge and you don't need it to play any of the content, so why add such a pointless tier at this stage in the game?