You can trim it quite a bit, and it also compresses quite well. The dependencies are the main issue, there's just a lot of stuff there.

Electron also compresses well but people complain about unpacked size, too. You're likely not going to see an embedded browser actually smaller unless you can disable features at compile time.

Does Servo still launch a herd of processes like Electron?

Doesn't look like it but if Servo wants to be a production-ready browser they will likely need to do the same. Better security and reliability having processes handling different roles.