I'd tend to agree, but OP_VAULT still has some nice features over what it's possible to do with Miniscript:
  • no need to roll the timelocks
  • spending from the main wallet can be easier, as we easily fall back to the hard-to-spend-from wallet should there be a breach
That being said, I think this theoretical limitations to sovereign veto constructs ease of use will be addressed in the future with things like HSM.
OP_VAULT definitely feels to specialized to be really worth a soft fork, at least to me. But from what I gathered listening to and reading O'Beirne, it is by design, as less contrived proposal have fail so far. Worth a shot, if only for the fruitful discussions that this proposal brings about.