In your second video your wrist is turned over on the follow through - facing up. This indicates what others are calling OAT. You are compensating with your wrist for the overstability of a disc, causing it to turn over or do a long 'S' curve.
Now - I can only point it out...I suck and am still trying to stop doing that myself. I got it better by throwing putters on a hyzer line out about 200 or so ...including my DX Birdie. If you can hyzer an understable putter far, then you aren't turning your wrist over - then work that into your other discs.
I found that after working for a while, the discs that used to be 'S' curve discs for me were running on hyzer lines all the time. Had to disc down to get back to distance.