I know everyone loves to dunk on Google, and I definitely agree their communication and customer service to app developers is shite, but this change to permissions scope is a good thing. If you have full, unfettered access to large number of people's Google Drive data, you're a huge target for malevolent actors. If you can't afford the new audit requirements (which I've done and are quite easy - if anything I'm sympathetic to the argument that they're more "box ticking" than valuable security audits), then I'd really question your ability to appropriately safeguard so much critically private data. For reference, these audits are about 1/20th as complicated as a full SOC 2 audit, for example.
FWIW I'm not previously familiar with this Transmit app, but based on their use cases (e.g. backup) it sounds like the limited "drive.file" scope wouldn't work for them. Still, if you want complete, unfettered access to my entire Drive account, I don't think it's a bad thing that Google is enforcing some minimal security standards.