First thing I'd do is double check they are actually the correct size. Do a shell check take your liner out of the boot and put your foot in with a sock on, slide your foot forward and measure the distance between your heel and shell. 1cm space is performance fit, 2cm is regular fit, 3cm is too big and you're screwed.
Secondly are they the right shape for you foot? The Descendants have a reasonably large amount of room over the instep so if you have a flat foot you may have too much room over the instep which is causing you to slip forward and get toe bang. Descendants also have a wider 102mm last and so if your feet are narrow and not taking up enough room you'll end up sliding forward and getting toe bang.
The other thing I would check is the space between your calf and the liner, you should be able to fit two fingers between your calf and liner, more than two indicate a sloppy fit. If you can fit more than two fingers you could look at getting a booster strap to try and tighten up the fit which could help keep you in place in the boot and prevent toe bang.
I like to ski with loose underpants or boxers on so my balls can swish around and chill.
this may not be your problem for you but after my first day skiing of the season I remember I need to keep my toe nails v short. I usually cut them once every 1-2 weeks throughout the year but during ski season I cut them twice a week.