When I first started I was a strict 1 credit runner. No credit feeding, no stage select, no savestates. Over time I have learned to embrace practice modes and save states, and think it is completely illogical to ignore the efficiency of this kind of practice. Let me give some of you an example of no save state practice that drove me insane. That was DDP DOJ. I would play DOJ as if I owned the PCB, I would never credit feed, and I would never stage select, each run began from the beginning.
It took plenty of time, and plenty of runs, but I finally was able to reach stage 3 with some consistency, and found myself praying for savestates/stageselect. Because there were certain patterns that would always catch me off guard, ones that I needed to practice, never the less, I persevered. Eventually I was able to make it to stage 4, and the concept of "hey go right back to the beginning if you want to see and practice the hard part" was driving me crazy. I was already able to get through stages 1-2 with complete consistency, it felt more like a chore. At the time I was also playing Gradius 3 with no stage select or save state or credit feeding philosophy, but then again, Gradius 3 even with credit feeding will destroy you because of the semi-impossible recoveries.
When Ikaruga came out for steam, and I wanted to 1cc it, I honestly couldnt have done that without stage select. I mean just imagine having to go through stages 1-4 ever single time just to practice the stage 4 patterns. I would have dropped the game like a brick. In fact I wish they would have also added the GC practice modes to the steam port such as choosing exactly which part of the stage to practice and also the slow motion mode. Anyway, these are games, whose primary objective is to be fun. I enjoy practicing parts of the game, if you don't you dont have to do it.
In regards to the fighting game metaphor. I have hundreds of hours logged into SF4, in all of it's iterations. I have friends who are very good at the game. Savestates and other forms of practice is akin to training mode in fighting games. training mode is not availible in pcb or arcade fighters. IMO all the best players have spent some extensive time in training mode. They do so to familiarize themselves with BnB combos and also familiarize themselves with the hitboxes/options selects/resets etc... (unless you're daigo or the other japanese players who basically spent a large part of their lives actually living in an arcade) They perfect everything in training mode, and then practice on a real opponent, and the game changes, it becomes about whether you can execute what you've practiced in a high stress situation. The same could be said for shmups. Clearing ikaruga stage 4 whether i practiced it or not, was very thrilling during my 1cc run. Even if I'd done it many times before, it was always thrilling. I think practice modes add to it.
TL;DR
save state and stage select is more efficient. Do what feels fun, this is a GAME at the end of the day.
To OP:
There are some shmups conventions that are universal. Play what you love, and perfect it. You will learn things like tap dodging and other shmup skills that are not unique to one game. Also not all skills are universal, for a beginner getting better at cave doesnt mean one will do well in old school shooters, nor does it mean Psykyo/raizing/(insert other dev here) will be a walk in the park. I would even go further to say that practicing one shmup means you will be a master of that one shmup. Overall skill in this genre will come naturally, there's no point of thinking about it too early, just have fun
