The U.S. diesel tuning crowd seemingly never discuss air/fuel ratios. This is a huge mistake. Also it's important to understand how much torque your transmission is rated for and to not stray beyond it. It's possible to reliably extract more performance than the manufacturer supplied but you have to understand what you're getting into. Turning it up to 11 and "rolling coal" is gonna get expensive, and it's super dumb.
Really depends on which crowd you're talking about.
The "I bought a tuner" or "I bought a kit" guys don't care or know enough to care.
Once you start talking about people who are reading turbo specs and whatnot people do very much care (because turbos and injectors are expensive and you want them both to be compatible so they get the most out of each other).
I disagree the diesel crowd doesn’t discuss air/fuel ratios but perhaps I’m misunderstanding something. Sizes and types of turbos, fuel pumps, injector nozzles are frequently discussed.
I do agree rolling coal is dumb but most/many daily diesel drivers don’t like it either, have always seen it as kind of a high school thing.
Maybe they've wisened up more recently but I've never seen an AFR gauge in a tuned diesel in the U.S., however they're as common as EGT and boost pressure monitoring elsewhere.
You can infer the same information it would get you via boost and EGT and whether or not your exhaust visually indicates unburnt fuel. You also don't need super precise AFR in a diesel like you do a high strung turbo gas engine.
Wide band O2 sensors are unreliably enough that they're kind of a pain to keep working accurately long term if you're not on a racecar maintenance schedule and if you aren't tuning things to those extremes you don't need that level of precision anyway.
Basically it just kinda adds up to "not worth it" for street vehicles
