I’ve had continued success with the SGSS progression on deads. I suppose it could work on sumo deads, too.
With your 200 kg max, it would look like this:
(Two workouts per week)
3x8 @ 140
5x8 @ 140
3x8 @ 145
5x8 @ 145
3x8 @ 150
5x8 @ 150
3x5 @ 155
5x5 @ 155
3x5 @ 160
5x5 @ 160
3x5 @ 165
5x5 @ 165
3x3 @ 170
5x3 @ 170
3x3 @ 175
5x3 @ 175
3x3 @ 180
5x3 @ 180
5/4/3/2/1 with 180 as your set of 3. You choose the jumps from there.
Repeat 5/4/3/2/1 for the next workout with less rest between sets.
Add weight and repeat the above workout for two more weeks (three total).
I confess that I treat the last week as a max out week. It’s 12 weeks of training and it can feel grueling but once you hit the third phase (the 3 rep workouts) you start to feel your strength growing and it motivates you (at least it does for me).