"The most important piece of equipment in your bag is your attitude" -Joe McNally
I guess we can agree on 1 point: Everyone learns photography differently.
There is no hard and fast rule I suppose.
I would feel it very restrictive to force myself to use only 1 particular focal length, and yet I do kinda get what your intention is.
anyway, as long as the end objective is met, ya?
It's fiscal discipline.
As ppl here say... Shoot, shoot, shoot.
One method of improving is to select the top 10 pics u take in a category eg. Portrait, architecture... And each time u set out on a photo trip, have the passion to beat your top 10 each time.
I feel imagination and composition still is the main skills in photography. Look at instagram n iPhone pics. Some are really good not because of the gear.
Sometimes the limitation of the gear gives the character of the picture. Eg. Vignetting, flare. These are not necessary bad things.