I don't use Symbiosis. it never really appealed because I always fancied a 'plainer' OS experience.
Never mind. I suspect that it's great for a lot of people.
My route was use plain Debian with Virtualmin installed to manage my domains and generally provide a nice GUI to manage all the config files for apache, postfix and all the other good stuff.
I've loved the experience.
However, every once in a while you have to upgrade the OS. I've done this many times but I'm always scared in case it screws the whole thing and all my customers are going to be down and out for a few days, or worse.
I too have migrated to a new host, instead of upgrading, but it is a faff, and I'd rather not do it.
My new strategy is probably going to involve Docker. And then (hopefully) as long as the persisted data is preserved with a backup, it's a half hour job to spin up a new host and deploy your containers + some time to let the DNS propagate if necessary.