I agree with you @nathansherburn , there isn't another reasonable solution out there. I use multi-account containers specifically to support access to the same service via multiple accounts. Even during development and support, it's useful to be able to be an admin as well as a user to verify changes in design, ACLs, conditional rendering, etc.
From the security perspective, multi-account containers + Cookie AutoDelete on all non-containerized tabs means that I get the best of more-private-by-default + persisting sessions when I need/want them.
I've paid for the Orion+ subscription for a couple of years, and a Kagi subscriber for longer than that. I still use Firefox on desktop all the time, because their implementation of multi-account containers. Orion on mobile is great, but when I need to do anything substantive there's no replacement for this feature.
Is there any way we can add Orion++ to allow specific features to get accelerated? When I asked back in March 2023, the target was 127 / 128. I would happily pay to make this finally land.