Why would you choose this gear for sprinting (or for anything, really)?
If the interval is too short for the trainer to ramp up enough resistance for you to hit your target wattage, then you probably need to use your big ring.
Direto is rated to deliver a maximum of 1,400W @ 40KPH or 2,200W @ 60KPH.
Looking at your Short Mix data from the 23rd, you hit a max of 888W on the third rep, so… plateauing isn’t really what’s happening.
FWIW, those are only 10 second efforts - and, yeah, it’s well known that Direto (and some others) aren’t great for big jump ERG intervals that short. If you’re working on those regularly, you’re better off using your big ring and switching ERG off.