For someone so new to the sport, you certainly show a lot of good sense in the right direction, FerretMan. Ideally a new rider should be mounted on a steady horse - one who has some go and tons of whoa, knows three gaits, and basically don’t know anything else. It should definitely not bolt, or shy, or evade a corner. Horses that do these things are dangerous, especially for a beginner.
However, from your posts, I’m not convinced that this horse is really doing these things, or your trainer is incompetent. I think what you have is a horse that is a bit too sensitive, and it has learnt to take advantage of a new rider. I think what might have happened is, you asked for canter, was surprised by how much movement there was, got tights (very very common and natural), and the horse responded accordingly.
For most tall riders, especially ones with tall torsos, a wider horse offers more security than a narrow horse. From this perspective, this draft cross is probably suitable for you.
With that said, I think something needs to be changed, or you will get seriously hurt. I’m not suggesting you to “get a different horse” or “get a different trainer”. This horse might be suitable for you with some minor changes. I would suggest you to do some canter on the lunge on this horse. That way, you can get a feel of what a canter should feel like without worrying about your steering. When you are released from lunge line, canter on this side of arena so you get a feel of it without worrying about him evading the far corner. Once you are comfortable, you can tackle the other issue.
You are athletic. Many factors are in your favor. You just need a bit time to get the right feeling. Trotting over pole on two points will also help you develop that much needed muscle memory that are lacking in any other sports. .