I went from around level 10 to level 29 (when Dominion released) playing unlocked half the time and locked the other half, for purple and blue respectively, because the camera angle is terrible when going south.
I come from a mostly-console background and never really played any RTS, so doing more with the camera than rotating it feels like a chore and I'm used to it rapidly moving. In fact, playing console FPS got me used to using strafing for fine aiming controls, so I use camera movement to line up shots.
Having the camera locked is more comfortable and lets me focus my attention and actions on playing my character, watching my opponents, and keeping an eye on the minimap, so having to unlock it negatively affects every part of my play, from overall map awareness, to landing skill shots, to learning my opponent's little quirks. I still won more than I lost (~1.2 W/L ratio in SR last I checked), so it's not that I'm incapable of playing unlocked, it's just worse. The unlocked camera just feels like extra unnecessary inputs that don't enhance the gameplay, kind of like if I had to alternate pressing two buttons to get my character to walk, but obviously to a lesser extent.
There is still the problem that the current locked camera angle is terrible. If there was an option for a rotatable chase cam, even with the current angle, I would constantly use that, even if most RTS players would find it unusable. Throw in an option for WASD movement controls and it would be even better.