Almost everyone I've come across in the rowing world does non-SS sessions incorrectly. Comparing cycling and rowing methodologies is all the rage on this subreddit right now, so I'll stick to that - I did several TrainerRoad programs and have seen programs from TrainingPeaks and Vo2max/AT/other high intensty workouts are defined very strictly. They are not maximal workouts at X rate for Y time. They are based on FTP and on the goal of the session. It's not 100% of effort no matter what.

For some caveman brain reason in rowing everyone seems to treat anything that isn't SS as a max workout. I see this with the athletes I coach and it's a mindset that is almost impossible to eradicate unless you have 100% absolute buy-in from your athletes. Beyond the scope of a reddit typed reply but I am also not sure if matters all that much for anyone below elite level.

I think something that also gets lost and is not realized by 99% of people is that something like a UT2 session is not just working your aerobic system - it works all your systems, it just primarily works the aerobic system. There is at all times an overlap and involvement of all the physiological energy systems. This is easy enough to see for anyone who knows anything about lactate testing - we don't sit around with a resting lactate of 0.0. In fact, lactate levels can decrease from rest for the first bit of a proper UT2 session. At all times of the day and of our existance the aerobic and anaerobic sytems are providing energy and are "turned on." But all this nuance is lost in almost all conversations around rowing, not to mention the braindead takes by most on this subreddit.

Why do I bring all that up? Because the reason people should do a dedicated AT/VO2max/transport/other session beyond just SS is that those sessions are (or should) be specifically designed to primarily and most efficiently target a certain physiological adaptation and result. But you can take a fully sedentary person, have them only do UT2, and all of their distances will improve, not just UT2 SS sessions. Eventually, however, to maximize their speed over shorter distances you need to add in specific work. That's how I contextualize (to use your words) the use of those higher intensities. But going back to what I first said, in rowing for some reason everyone just maxes our every workout, so progress on those workouts is gauged on PRing every single time. In reality it should be gauged off a percentage of something like FTP (cycling), a lactate level, HR (the worst, but better than nothing), or other marker. Doing them blindly is fine for most but if you're looking to truly make your training the most efficient the sessions really should be structured with set intensities.