How long are you in this party? If in your experience you find that it’s possible to alter some policies of the party, then it’s definitely worth it struggling from the inside and fight for a more revolutionary line, even if it’s not a “ML” party. I expect however, that sooner or later you’ll find something in the party that cannot be changed because of limitations of the organization.
Arguing that there’s not much to be done is not that useful. There’s always something to be done. The South African apartheid lasted for decades, but it was eventually over too.