> Finetuning isn't reverse engineering

Fully agree, it isn't. Reverse engineering isn't necessary for modifying compiled program behaviour, so comparing it to finetuning is not applicable. Finetuning applied to program domain would be more like adding plugins or patching in some compiled routines. Reverse-engineering applied to models would be like extracting source documents from weights.

> Finetuning is a standard supported workflow for these models.

Yes, so is adding mods for some games, just put your files in a designated folder and game automatically picks it up and does required modifications.

> Also, the "redistribute" part is key here.

It is not. Redistributability and being open source is orthogonal. You can have a source for a program and not be able to redistribute source or program, or you can redistribute a compiled program, but not have it's source (freeware).