There are two schools of thought here, and I'd err towards the one you're arguing against. There is the school of thought that says we need to do exercises that are uncomfortable until they become comfortable, and we develop strength, suppleness, etc. Then there's the school of thought that says that piano playing actually requires almost no strength, and we should be looking for the motions that are effortless, from the get go, rather than building strength.
Obviously there has to be some balance between the two, because some composers write stuff that simply isn't pianistic, and does require strength. But, on the whole, the latter argument is more important. There are 12 year old kids who can play the big repertoire with more apparent weight than I can, and that's not about employing strength. It's about first finding the right way to transmit arm and body weight to the keys, and secondly, relaxing. Things do become faster and more comfortable, because muscle memory is a thing - but we shouldn't really be persevering with movements that are uncomfortable.
Having said that, the usual fingerings given for scales shouldn't be uncomfortable for the vast majority of hands.
Well, I was not really talking about strength, but rather flexibility, and I'd not say playing the piano erquires no hand and finger flexibility. Untrained hands will find even basic arpeggios not confortable. If a beginner decides on his/her own what fingers to use (we all started with our sole forefingers to play a melody
), that might work at the beginning but they'll eventually come across problems.
When playing fast, very slight movements make all the difference. As you stated, wrist, thumb position, raising the hand to make it more vertical for some passages, using one's forehand, elbow position, and getting rid of tensions, etc. Many fingerings are actually unconfortable because we keep tensions in one finger that project to another, not because they are unconfortable on their own.
Ultimately, if you set fingering strategies that let you play without constraint, that's not a problem. Who cares if the work is performed as expected? But I wouldn't let a beginner set his/her own strategies unless there are specific reasons (very small hands, etc.). A friend of mine learned on his own, he can play well, but he developed a strange habit: instead of using his thumb to move up on a melodic line, he passes his ring finger above his pinkie twisting his wrist. And he can do that several times rather fast to play several notes up that he didn't anticipate. But I'm not convinced he developed a good strategy... Once he'll want to play licks and runs, he'll have to learn how to use his thumb properly.
From my experience and from what I was taught, I admit I have a little hard time conceiving piano foundation differently, but I could be wrong. People are different, and other strategies might work well for other people. But keep in mind that the OP asked for advice as a beginner, not as an advanced player who can adapt his/her fingering for a specific passage to make it easier to play, that's another subject I think.
