I come from the piano side of things, but I do play a bit of guitar, and the same basic musical building blocks apply to piano and guitar. I personally do think scales are fundamental, especially if you’re going to do something like blues improvisation. Basic blues is a good place to start, and the patterns on the guitar (the “blues boxes”) lay out rather nicely under the fingers. If you learn the basic patterns/scales and commit them to muscle memory, you’ll be able to know what notes should sound good, be better able to connect from riff to riff, to improvise, etc. Eventually, after you become proficient, you should be able add notes outside the standard blues scale to taste. But many, many rock solos are just based purely on the blues scale for the key. If you start playing through many transcribed rock solos (via tab, ear, or musical notation), you probably will end up figuring out the patterns anyway. But it’s nice to know where the “right” notes are without thinking.
When I first learned to improvise via the blues, I had no idea what I was doing. I didn’t even think it was possible for me to learn. I just thought it was something that came natural to some musicians and others just struggled at it. I picked up a book that taught me the basics of the scale, a few examples and riffs, a background accompaniment (in this case, just a basic root-fifth, root-sixth quarter note pattern for the left hand on the piano), and then I just started playing around with those notes. Through some trial-and-error, and through listening to how other musicians strung these notes together, I started piecing together how to play these notes together. Knowing the scale and the pool of notes typically chosen from in a solo made it a lot faster and a lot easier to learn and mimic solos on my own. It took a lot of “noodling” around before it started to sound good, but that sort of playful learning period where you’re trying different things and experimenting I feel is important in learning to play instinctively. (At least it was for me. I’m not trying to say my method of learning is THE method of learning or that it will work for all people. And learning scales helps this along, in my opinion. It helps to organize the notes and it becomes easier not to hit the “wrong” notes because you know if you’re in, say, the key of E, that E, G, A, (A#/Bb), B, and D are all “safe” notes to choose from.
If rock and blues is your interest, I would start with something like the minor pentatonic (E,G,A,B,D), then once that is comfortable, add the A#/Bb. Of course, with guitar you also need to learn which notes are good for bending and how far you can bend them. Over time, through listening to others solos, playing through them, and experimenting on your own, you’ll figure out these patterns, and how these bends sound in context.