The point is that the post makes it sound like using a Pixel 11 under Android results in less security than before, but for most people there is no change since they never used MTE anyway.
That's not what they're saying. They're saying Graphene without MTE is less secure, which isn't something they want.
Which you can read from their post here
We strongly recommend against buying Pixel 11 devices. Pixel 8, 9 and 10 have much better overall security for GrapheneOS. Pixel 10 is cheaper with similar hardware and MTE. Pixel 11's Titan M3 should improve BFU security for users without a strong passphrase, but losing MTE craters AFU security.
I think you misunderstand what is being said.
That's not what they're saying. They're saying Graphene without MTE is less secure, which isn't something they want.
Which you can read from their post here