I don't like it either, whole L7 matching is more hack than proper tool (but that's an opinion anyone is free to disagree with).
If you use it as substitute for
conditional forwarders (a feature MikroTik didn't implement even ten years after it was
requested, even though it's nothing special, I'd say it's pretty basic thing), it mostly works and usually you have just one domain, so it's one rule and that's it. Not great, but not too bad.
In this case I understand that hostnames with different domains would be used, so there would be L7 filter for each, which makes it a really messy solution.