I agree that people should practice with drivers, as throwing mids and putters shows how to not torque the disc and be clean, but it doesn't show how to throw hard (like a driver does), or nose angle sensitivity. The "don't throw drivers!" thing is, to me, mostly for beginners who buy a Blizzard Boss, or guys throwing 300' like I described where no disc mattered.
My experience with high speed stuff began with a star Vulcan. Initially when I was throwing in the no-snap barrier that I desribed, I threw the Vulcan with some torque and lots of speed (I was trying to be clean) and I could get it to do a crazy S-flight out to 380'. It was crazy, like 50' farther than I had ever thrown. I thought high speed drivers were automatic distance.
But, I cleaned up my form and couldn't throw the Vulcan for months...it would hyzer out every time. It wasn't until I got to that 350' mark with some snap that I could throw it again. Then over time I found it's too flippy to be reliable once I have the "real" arm speed it takes to throw faster discs somewhat properly.
So I wasn't saying never throw high speed stuff in my original post, and it was very good I had a disc like that to measure myself against....but I just didn't want to list any distance benchmarks with it at those early stages because it was so unreliable depending on the day and how much torque I had, until I could throw it more properly. And at that point throwing something more like a Destroyer gives more repeatable results.
As far as the putter distance thing:
In my first week of strong arming discs I could max out at 300' occasionally, and mids were already going up to 270'. I went through so many form variations and added 100' to drivers with mids only going ~300' in a trustworthy way (I could throw them 330' on the field occasionally, but more often than not they would act too flippy if I tried to overthrow them). I could throw putters like 230' pretty easily initally. I saw barely any added distance with mids and putters (putters up to 275' consistently for a long time...with absolute max rips to 300' occasionally but they felt different).
The thing I found is that if you're clean with a mid or putter, they float out there 250'+ very easily. You don't need to throw them all that fast, or have the nose down really. Once you get to the snap area of technique they'll fly out there way straighter...but they may not go insanely far. But, if you don't have the arm speed that doesn't necessarily translate to high speed discs. If you can throw a driver 400'+ you can definitely throw your putter over 270'...but if you can throw your putter 270' you can't necessarily throw your driver 350'...they have a bit of a different technique and arm speed requirement, and drivers need practice too.
I fully agree about throwing understable discs too...best way to make sure your planes are consistent and learn some shot shaping. Throwing neutral putters, neutral mids, straight (stable) fairway as well as slightly understable fairway drivers, and something faster that isn't beefy is the best way to get all of the variables of different throwing requirements IMO.