That’s because armor of higher level has higher Azerite power requirements than lower level armor. That means a shiny new piece of Epic gear will have better stats but, unless you’ve been diligent about your Azerite power grind, won’t have as many traits unlocked. You lose options as you earn better gear. Eventually, you’ll grind out enough Azerite to earn those traits back, but you’re left with limited customization until then.
While the proc is random the law of large numbers will mean that over a large enough sample size your actual yield will be the same as the average proc rate. If you transmute 10 times then you can't rely on the 20% proc rate, once you pass 1000 though, you're average will start approaching the true rate of 1.2 bars per transmute. If you are in this for the long haul it then makes a lot of sense to use the average proc rate to calculate your profits, especially considering the fact that all the items involved sell really well.
Thing is, as in real life, opportunity cost is the real key on this. I'm getting 2 tokens per month quite easily with just 3 toons (1 maxed only (yeah, pretty damn inefficient but I lack a lot of time to play :p)) just by flipping couple of things, food, flask, potions, bags, shirts (yeah, shirts!!), etc etc. Every damn penny/gold counts :p, just have to learn how your realm market works, what niches exist, which items are needed and undersupplied and which are oversupplied.
That's where i'm at now. I got into it late. I had 40k to start. Sold fish up to about 100k total starting capital. Started making and selling decks when they were going for 80-200k on my server. Morons have repeatedly undercut decks by 30-60k at a time even after the market has been reset (not by me) multiple times. Now the decks are 25-80k... I did manage to make 3.5m gross in the last 2 weeks. Now the individual cards are selling for MUCH less than the decks so I may stop crafting myself and just start buying the individuals... idk where to go from there though. Do you think the decks will hold any value moving forward? I'm kind of hoping for something similar to obliterum in legion to increase the ilvl and keep them relevant.