You know you can disable free aim while locking on in the prime trilogy? Atleast for Prime 1 and 2.
For some bosses in Prime 3 you needed the free aim, but it's not that hard to point the crosshair in the middle of the screen when you didn't need to shoot at some other enemy body part.
Granted I never owned the GC copies, but I was kinda embarrassed after looking in settings and going "huh, you can do that?". Took me like a few years to find lol.
Granted I prefer the default. I enjoy being able to strafe but still shoot whatever. There are times where I have locked on to enemy A to shoot other targets/enemies first, so it's pretty useful.