IMO, 1Password has much much better UX than Vaultwarden has. So you definitely get something for the money.
We are talking about $5k/month vs $500. If the UX of the FOSS version is lacking, pay for the closed version BUT throw $1000/month on the direction of the FOSS developers until the issues are mitigated and they satisfy your requirements. I can bet that in less than a year you'd be able to make a switch and the investment would pay itself.
This is not at all an easy thing to guarantee even if you’re willing to spend the money. The FOSS developers might not be interested in doing this work (even for pay) nor have UX staff.
So many talented people working for that money or less in São Paulo, Buenos Aires or Hanoi, it would be worth it to give it a shot even if they just worked part-time.
In all three cases, though, it sends a signal that there is demand for the changes. This works as both validation for the developers (our users wants this so much they are paying someone else to do it) and also for other companies (oh, why should we be paying this much to a closed-source service if we can pay a fraction of the price to get a reasonably-well-supported open source version?)