Problem is tailwind is not hard to maintain. I would argue it's easier. Folks look at it and it looks like a nightmare (the documentation even says so) but you have to actually give it a fair shake. I can always jump back into a tailwind codebase and not only do I know what mr-4 does I know where it is when looking at the rendered component.
You find yourself having to do "Right click > inspect" a whole lot less often to figure out what's going on
Tailwind is not easier to maintain than vanilla CSS in any way. There are no standards in Tailwind, tomorrow if they wanted they could rename everything. CSS actually has standards to adhere itself to. On top of this, Tailwind has to go through a process to adopt bleeding edge CSS changes, which makes maintenance a chore when you really wanted that new feature.
Tailwind is not easier than a custom internal design system either, as that has been tailored to your company and the maintenance of that system is integral to your design team. You might think that offloading to Tailwind is better, but you're just doubling up duties because someone internally is going to have to customize away from the defaults.
Tailwind can be easier to maintain than similar libraries. After trying most of these, I can't say whether that actually shows itself during development. I suppose if one was exclusively used to Vue or was brought up in the world of overzealous BEM, Tailwind might seem easier/refreshing. But if you've worked with Bootstrap or its alternatives (of the time), Tailwind isn't much different and can feel like a step back when you now have to rely on additional libraries like Konsta, Daisy, or Tailwind UI to create premade components for you.
Your example confuses me too, because why wouldn't your devtools be open anyways? You're in development so use the tools you have to make your job less of a guessing game. I guess what you say might be true, you can load a page and just tell a component has a margin right but you're going to be opening the devtools anyways to double check.
I still think Tailwind is great for solo devs, it's a design system with sane defaults they can rely on and get something in production very fast. Every other reason I've seen Tailwind devs give winds up confusing me about how they're actually working, or if they've ever bothered with anything else.
You find yourself having to do "Right click > inspect" a whole lot less often to figure out what's going on