M105 is not something I'd reach for on Subaru paint.
But then again M105 is not something I'd reach for on any paint nowadays.
The problem with Subaru paint is not so much that it's soft (it is), or thin (might be), it's that it can be sticky. Certain compounds and polishes just don't play well with it.
I've had success with the newer Sonax polishes on Subaru paint. I can't remember if it was Menzerna or the now discontinued Optimum polishes that stuck like glue after 10 seconds of buffing.
If the test spot looks good, you need that level of correction, and you're not finding that the product is sticking to the paint while polishing then go for it.
Are you planning on following it up with a second step? I've never had M105 finish down well enough for LSP. I'm sure someone has but my guess is they may have different standards than I do. I find it hard to believe that it'll finish down nice enough on Subaru paint.