Great to try and learn something new. That being said from your question I asuume you DON'T Event. And you don't say which levels you are talking about but this is not including Intermediate and Advanced.

1. False-Most horses are under trained for the actual tasks at hand because most riders/trainers have an ego problem and a desire to move up the levels before they are ready to do so.

2.False- They have actually shortened the x-country phase to be able to use less land and give some of the european countries with heavier breeds a fair chance. The actual Jumping part of x-country which every sees is/was a very small portion[ 1/4] of the total ride. It starts with phase A Roads and Tracks, designed as a warm-up it is a distance of 4400 meters ridden at a speed of 220 meters per minute=steady trot/ slow canter. Phase A ends at the start of Phase B steeplechase which is 2760m ridden @ 690mpm=very forward gallop. Phase C Roads and Tracks blends with B, slow down after the last jump slowly come back to walk for a few minutes[apprx 5] distance 8800m ridden at 220mpm. That ends at a Vet box, all the horses vitals are taken,he is jogged in front of vets for soundness,equipment can be changed...That is a mandated 10 minute hold. Which then starts Phase D Cross Country-with the fancy jumps that everyone watches. So, since they are only using phase D horses should be much sharper and less fatigued- If the proceeding training was done correctly.

3.True- Although not the whole coarse. With new technolgy comes new trends. They have taken some of the monster fences which if ridden straight forward in balance were not tech. demanding and replaced with opticle illusion or corner,bending line,terrain falls/elevations,narrows. But again if ready to be at that level, its what you are training at home, it is easily done.

4. Its all rider error. Everytime you sit on a horse it is your job and responscibility to give him the best possible ride. The more consistent your balance is the more trust the horse will have in you and the more mentally relaxed he will become. Even a minor balance problem, the horse becomes unsettled and will defend himself becoming tight and resistant which leads to the "simple" mistakes.

5. The optimum times haven't changed. You can go back years and read the descriptions in the old rule books and the standards are the same now as they were then. And you get penalized for going to fast as well as to slow.

False-There is a huge increase in falls/accidents at the lower levels. Due to ill prepared horse/rider combinations. This is not a sport to be taken lightly or just try on a weekend. It is a demanding sport where both horse and rider need to be fit[yes I said it-NOT overweight] and mentally prepared. If/When done correctly, there is a very low accident rate.