I see a couple of things.
One is you're crashing down. Don't lose control of your descent. Put the breaks on and ride into a smooth, deep bottom position while fighting to maintain a tight chest and upright torso.
The rounded back is called a butt wink. It's a soft position that is very common but should be corrected with mobility work. It's probably tightness in the hips, flexors, psoas, or possibly even glutes/pria formis that is pulling your tail bone down. Work with a field hockey ball will do some good. I would also load up like 135# and just sit in that bottom position for :30 seconds with relaxed legs, knees out, and a tight, upright chest and let that true bottom position sink in and loosen up. Do that a lot.
I also see your midline/core breaking down as you come up out of the hole. This will likely resolve itself over time as you squat more, but you should work on midline stability to correct this as well. Core stuff. Loaded carry. Back. Abs. Planks. Rows. Swings. Pulls. Deads. Squats.
Until stability and mobility improve you should readjust your expectations. Power is not holding you back. The speed of the movement shows that. You need to mobilize and stabilize and then you'll be doing sets of 3 with 200+. Maybe a shoe with an elevated heel is in order, too.
Coaching cues when you squat:
Set the chest. Push the hips back. Don't let your midline posture bend.
Put the breaks on. Ride into the bottom. Not a free fall.
Keep the chest tight and upright. Fight for that position.
Explode up out of the hole. This is where you want to see speed in the movement -- on the way UP. If you need to "lead" with your sternum to avoid rounding, do so.