To me, the appeal of Joplin is its openness. It's open source, I can encrypt my own data and store it wherever I want, and I can and hack it to do cool stuff. In terms of functionality, it is strictly inferior to its competitors in my estimation, but that's OK, since this deficit outweighed by the fact that it's open source. A "nerd-tool" like hi-ko said.
I don't think a restrictive license on any part of the project is a good idea, when the project's primary "selling point" is its openness (assuming that most other users are like me, and value openness over raw functionality: otherwise we would all use ever-note).
I understand your concerns, but don't think they are realistic. I don't think a significant number of companies will start hosting commercial joplin server instances while Evernote exists. It's just not going to happen. I don't expect a restrictive licence will do anything to preserve reliability.
Since you explicitly except personal use (which is what I expect the vast majority of Joplin users are doing) I don't expect it would really hurt the project either? Just seems silly.
So I don't think I can really donate to something which explicitly detracts from what I like about this software (even if the detraction is very minor). I will just keep up my regular monthly donations to support the development.