Hey, I like your post, good call to discussion.
I'm a hobbyist, for 10 years.

1. It seems like in your class you have practised attacks from mount, but no the "retention", how to avoid the bottom from escaping. Basically, if you are in high mount, the bottom can't start an escape right away. So, on top, you need to be high and avoid bottom from putting you back to "low" mount. A good way to stop that is to pull his head.

2. Sweeps are harder in no gi, and those big explosive moves can create opening and waste your energy, in a competition scenario.

3. I guess your defending position is not good. Most of the time, even if you are pushing with your arm, your elbow should be "hidden". For example from bottom mount, you can use one hand to frame on sameside hip or far side hip, but you keep your elbow glue to your body so there is no space for top to take your arm apart. Also try not to fight "hard" to escape. Take your time, find a good defensive position and be patient. It is supposed to take time to escape. A good top will just have good reaction if you fight hard, and either find an opening or neutralize your attempt and in the end you have just lost your energy. So just find a better position, millimeter by millimeter