I went to a stiffer pick more quickly than you. It took some getting used to, but I liked the feel and sound of it better than the soft nylon. My pick grip just sort of started to work well kind of “over night”. I had trouble and then I didn’t a few days later.
There are subtleties in your wrist rotation and string attack that I don’t seem to have earned by conscious thought, but more from playing. Once your string attack gets a little more ironed out in your mind, the pick won’t spin so easily and you find you lighten up on the grip or squeeze harder to change the force applied to the pluck/strum. Initially, I was digging in deeper with the pick and that isn’t necessary for me too often, I just need to grip tighter or looser. Your strumming looks pretty good now and sounds nice. I don’t see much wrist rotation, but it is not much, so hard to tell in a video. It probably won’t take you long to get used to the stiffer pick.
I find I tend to go for the Dunlop orange (0.6? paint worn off!) for general purpose playing and something thicker/stiffer for individual note picking. You will start to see some of the individual note picking in grade 2 and more in grade 3. for super stiff look at the Dunlop Glide. It has a really nice feel across strings and keeps the hard edge to the release that makes notes stand out. Watch for a sale - they are expensive for some reason. I can strum with the 2mm Glide but it certainly is not as comfortable as the orange.
If you haven’t yet, get a couple sets of variety packs. I found I did not like the sound of the nylon, no matter the thickness, so trying out a bunch of picks was handy.