Indeed, which is why I would consider acquiring a starter. You could include Velasquez in the deal (which saves you $) or view such a move as something that also upgrades your bullpen by leaving VV in there permanently.
And that also gives you the flexibility to use Howard there when he's not the spot starter, especially since that would be his role in the playoffs anyway.
I don't think the Phillies should feel any obligation to prioritize Howard's usage and development, the season is already completely weird and how he spends what is now a mere four weeks remaining - consistent 5th starter, flex guy, even going back to Allentown for regular work - isn't going to significantly change his track for 2021.
5th starters are generally not that great but if you're really embracing being a contender in this weird season, and 1 game makes the difference between 8/9 or 5/6, Howard and VV's results are no more acceptable than Hector's.
The bigger issue is you still don't want to pay a normal prospect price for a clear rotation upgrade. But who knows what normal's going to turn out to be.