Regarding front or rear brake, you have to understand what brake does what and when to use which, which combination and what amounts. Touching your rear brake while already braking hard will just make you skid since the rear tyre is already almost lifting off the ground. The majority of braking is always done on the front since there is much more weight and traction while braking there.
However, when on loose or wet surface, if you brake hard at the front the rear won’t lift, the front will wipe out and you’re on the ground. So loose/wet surface is totally different from dry asphalt with sticky tyres, as is cornering on loose surface (mtb) and road bike (asphalt).
Once again, motorbike techniques. Most cyclists are slow in corners, no matter ftp or what category they’re in. I always rest in corners and still leave gaps behind me. (I rarely brake in corners at all while on a bicycle, unless I see gravel or other dirt. On a motorbike there’s always a lot of braking going fast into corners.)