The upgrade path is a path, ultimately what you need to get a feel for is how fast/powerfully you swing and then given that, what rubbers suit that swing speed and contact depth and then try out those rubbers. While as an EJ I have used a lot of rubbers, the most importabt thing ultimately is the time spent playing and training with the rubber.
When I started working with my new coach (who unlike me got significant training as a child and is significantly stronger than I am), he asked me what rubber I used and we both use the same rubber on different blades. And then he asked how I felt using it and we spoke about how rough the transition was initially but how now, it is so natural we just enjoy it even with some of the pains (I still need to train much more against no spin players).
My main point is that the most important thing is not the upgrade path but how fast you swing and whether your training hours let you get confidence with the rubber and its quirks given your instincts. All the major Butterfly rubbers from T05 to Z03 all appeal to largely the same kind of player with nuances here and there based on how you really like to score points or defend points. My playing level wouldn't change much with any of them, but how I feel and the shots I would attempt would be affected by each because they can make shots feel subtly different and make someone mlre confident playing a certain with one vs another on certain shot selection opportunities but not to the point where you are not the same player. Of course the blade matters as well, but ultimately, just pick whatever you want to commit to a use it. I know kids with offensive offensive styles who started playing after me (and are better players now) who still use T05. My last coach was on the Swedish national team hierarchy before retiring to face a regular job and he used T05 when he last played because he preferred the way came off his paddle to Dignics 05, even though he could clearly use either.
The main issue is using rubbers that are too hard to accommodate how you usually like to swing or too soft to let you maximize your swing speed and feeling. If that is a concern, try before you buy as much as possible. This is more important than some official Butterfly path.
I agree that an "upgrade" path is just a path. But among your points, I think I agree more with spending time with the rubber you choose. Then when you know it thoroughly, you can fully enjoy all of it's aspects. For me, there is no too hard or two soft, maybe because I didn't really have a choice, so I just adapted.
My own path started with a department store pre-made for less than $5. It was a shakehand blade which I used with penhold style at my middle school club. This worked fine for a year learning all the basic strokes.
Then a schoolmate showed up with a jpen and butterfly sriver. I tried it and it was simply amazing. There was no need for adaptation time. I simply leveled up immediately when using it, so I ended up getting my own through my friend's connections. This setup lasted a good 7 years. Then I stopped playing.
After 6 years, I started up again when my work place had a table. Still using the same old jpen with the same sriver rubber, I played 11 years casually with work colleagues. I probably never improved much. But I could play, and it was fun.
I changed work and this was the era of Tenergy (05 more specifically). Here people were much more serious, and that was when I started getting more serious too. People were of two camps: you either played with Tenergy 05 or Hurricane 3. I had started watching pro matches, and my favorite players were all using Hurricane so I fell into that camp and started all over with a shakehand blade (Clipper was recommended) and Hurricane rubber. My work mates would play at a local club, so I joined them. The style and technique was all new, but I would say if you just practice the fundamentals slowly, you can learn a new style. It's never too late. There were players of all levels using either Tenergy or Hurricane. I've been playing with Clipper/hurricane for 12 years and never thought I'd ever change anything again since I've improved so much and play so consistently with my setup.
But recently I was gifted a used sheet (6 month old) of Zyre from my colleague and I thought it would be something fun to just try. After a few weeks, I'm surprised that I can do everything I could before but with much more ease, so I'm probably going to make the switch. After all these years, I ended up with Butterfly again. Butterfly path?
