Shadowboxing is the best thing you can do to improve technique imo you improve so much more doing it against a mirror than you ever will skipping rope or hitting bags. You can never do too much shadow boxing its the best thing you can do aside from actual sparring in terms of improvement.
Mate that trainer is a spastic, find a new one. You can't tell someone to hit harder or faster, if he's got you consciously trying to do that it's going to have the opposite effect. Everybody is teachable, the only question is do you have a good teacher? If you do have that and you want to learn then there's no reason why you can't become a proficient boxer if you have a functioning nervous system.
I'm of the opinion that most shadow boxing should be done away from a mirror, you can become a bit reliant on visual input instead of proprioceptive input from the rest of the body if you always use a mirror. Shadowboxing with eyes closed definitely helps get the feel right.
I agree with this, mirror boxing also makes you to static as you need to keep facing the mirror. The mirror is useful to quickly check out your form but you don't want to be in front of it for prolonged periods of time. Shadow boxing away from the mirror on the other hand cannot be done enough and I really think you should be doing it for an hour or more pretty much daily especially when your first starting out.
Power comes from the mind as much as muscles, what was your childhood like?Mine was full of abuse and living in terror and when i think of that the hate builds up and comes out in my fists - hard.
How would you split it up ideally? If you were doing half an hour would you split it up into say 7 x 3 minute rounds with a 1 minute rest period after each? Something like: Round 1: Warm Up Round 2: Footwork / Movement Round 3: Jab Round 4: 2 or 3 punch combinations Round 5: Defense Round 6: Numerous combinations and vary speed Round 7: Combination of the above?
There is no ideal way, mix it up and experiment, find what works for you and be ready to change it down the line. Right now for me personally I am doing 3 minute rounds with 1 minute rest and I just fight and try to keep it all like I would do in the ring against a real opponent. My focus then often changes based on my most recent fight/sparring experience. For example on my last spar i kept getting caught with right crosses and so now as well as all the things I had been doing previously I am working on certain things my trainer showed me to avoid getting caught with that punch and the counters to it so my body knows the answers next time.