The progression you outlined for strength.... 80-85% 6x2, 6x3, 6x4, then 10x2 and moving into sets with 90% and finally 95%.... Am I doing one block, i.e. 6x2 or multiple blocks (6x2 and 6x3 or 5x2 @ 90%) per workout? If I do one block it doesn't seem like a ton of work but if I do multiple blocks I can see it becoming overwhelming quickly.
This progression is addressed over several weeks, starting with 6x2 (of a particular exercise) and eventually working to 6x4 as strength increases. Once 6x4 becomes easy you have increased both strength and some strength endurance, now you can make a couple of different changes:
1) Increase the load and drop the reps back to 6x2 to go further in the direction of pure strength (make sure to adequate rest enough between sets that you can complete all of the assigned work)
2) Maintain the load but make part of it from chain so that load increases as you move into more mechanically advantageous joint angles, reduce the number of reps, increase the number of sets (10x2) and execute each rep as explosively as possible to steer the training effect in the direction of power. The chains will allow a smooth acceleration.
3) Maintain the load and drop the reps back to 6x2, change the execution of the movement, i.e. if you have been doing full Back Squats, do Dead Stop Back Squats, i.e. from the standard starting position lower the barbell to rest on the rack’s safety bars, thighs should be below parallel at this point, relax, lose contact with the bar, then reset under it and start the Squat from a dead stop like starting a Deadlift. This will reduce the max load you can Squat but teach you to turn on and drive, drive, drive from a compromised position.
Make sure you have a true 1RM for the movement in question otherwise 80-85% isn’t meaningful. And you’re right that 6x2 @ 80% with one minute rest between sets is not stressful in a cardio-respiratory sense but if you use a true 1RM and use 80-85% and Squat to a depth where the thighs are parallel or below the 2nd rep on sets 4-6 will be tough, or it should be.
So the idea would be to pick several complementary exercises: Squat, One-Leg DL, and an overhead movement like a Push Press or Jerk. Warm-up, then do the 6x2 in each movement. This will be a meaningful day. It shouldn’t destroy you but the point in any strength workout is to cause enough stress to stimulate adaptation without reducing training frequency by making it hard to recover.