If a horse is scared of fences, there are usually more than one contributing factor - over faced, introduced too quickly, and the rider is not supportive and solid themselves to help their horses over the fences.
If a horse is rushing, and heavy and is blasting through the fences - again, there are contributing factors. 1, rider error in form and posture. Riding hands first and not seat first. 2, horse is heavy and unbalanced.
Most horses just get their job done regardless of how incorrect their riders are *shoulders dropped, forward upper body, no seat, lower leg not stabalized, jumping ahead, looking at fence, looking down etc, etc, etc* and just do what they know that they have to do - but then there are horses that say "uh uh" and reflect what their riders are doing.
I would first, look at the rider and see what it is that the OP or anyone who has a speedy, rushy horse - what it is that they are or are not doing, to aid their horse.