So your fat bike is overgeared. There are ways to fix that by using a lower gear...oh, wait! Shimano and SRAM have determined that you don't need those gears 'cause their racing team doesn't need them.
I suspect the fat bike is under geared because no one considered using it as a touring bike when designed. But never the less, Shimano didn't determine anything as an easily ordered 11/42 cassette just arrived in the mail yesterday and awaits it's place on the fat bike. I know what I'll be doing over Christmas.
Herein lies the problem. The 48/31 with an 11-34 has a similar range to the outer two gears in a 3x system but range isn't everything. Look at
a comparison of that set up to the same cassette with a 48/36/22 triple. The 2x suffers from the same problem that all wide range 2x suffer from. It's two different drivetrains with little overlap. Consider the 21 tooth cog on both systems. In the 2x system, there is a 22 gear inch gap and a 10 mph speed differential between the two rings. In the 3x system, there is a 15 gear inch gap and 7 mph differential. The transition is smaller in the 3x and feels more natural.
I am going to suggest the differential is just because you are used to one system. If you spent time riding the 2x system it would also, become natural. Sometimes we make too big a deal out of what we perceive as "optimal" conditions.
But the big problem is that the 48/31 2x system doesn't even come close to a 3x system for range because the 3x is so much lower. To get the same range as the 3x system, the 2x would have to
change to a 48/22 which makes the gap even worse. Of course, you could go with a smaller outer ring but then the range is much smaller. You have the choice of having good low gears or having good high gears but you can't have both. And, considering your first paragraph, your 22/36 is too high, how does having a 25" low instead of a 16" low make anything "better"?
But, you might say, you can change to a larger range cassette. Sure. But what is keeping me from doing the same with a 3x system?
Not really sure what you said there but you seem to gloss over the fact that the older 3x systems you prefer came with cassettes that maxed out at 36T. The newer 1x and 2x systems can come with 42T+ so it's not a straight across comparison. In the example they are comparing race oriented bikes so they have narrow range cassettes. But yes, you can add a wider range cassette to your triple.. apparently you are suggesting Shimano and SRAM don't dictate what you can use.
You are offering a bit of a red herring yourself. I didn't address the cost of a chain or chainring. I agree that those are fairly inexpensive and just part of riding a bike. The cost difference of the
cassettes is an entirely different matter.
I didn't offer the example, I just said the occasional replacement cost did effect my decisions. The same with cost differentials. There is also quite a cost differential between some brands and Compass tires, some saddles and Brooks... yep.