I thought to number your questions for easier answering. Here are my thoughts.
1. Yes and no! Many self taught players acquire great skills in playing. But being taught musical content based in harmony, rhythm, and melody is the only proven academic approach that gives everyone the same chance at improving their playing. That is EVERYONE! To what degree and in what capacity those lessons will benefit you isn't predictable. What is predictable is that if you practice these things regularly, everyone is going to play better.
2. Being self taught (and all that goes with it) coupled with being taught top musical academic principles is the entire experience that has grown 100% of every bass player that ever played a bass guitar. The only assurance that you can have that you will learn how to play your bass is by practicing musical content. But this isn't realistic because practicing academic music has no impact on anything outside of the academic experience. You have to be self taught to complete your musical development. Finally, if you are asking what that specific material is and what the specific manner of teaching it is, ahh, now you might understand better how bass educators have not fulfilled their obligation to their students. I can't describe to you what to practice in detail because I don't know what you musically know. But the specific method of practice is easy to describe: Practice your written material every day. Do it out of time if needs be and tap your foot. Don't use a metronome. Fix your mistakes when they happen. Review! Review! Review! Take breaks because you will be in a mind oriented learning eexperience and this can feel tiring. Don't warm up. Just play! Never play until you are exhausted or uncomfortable. Pace yourself. And do this every day. But remember that even God took a day off. You can as well.
3. Rote exercises are valuable if they contain irrefutable musical harmonic and rhythmic perfection. Reading as well, but you should be aware that music of what is touted as valuable reading isn't really beneficial for bass players. The Jamerson book comes to mind. Etudes based in solid harmonic and melodic principles are great. Scales and modes are overrated so just be aware of this. I hope I helped.