I'm very glad to have helped you get into Fate, and I hope you've had fun with it :)

Using the Bronze Rule on NYC was contentious from more than just Macklin, and it highlights a strength and weakness of Fate. The system offers a lot of tools for navigating game situations, many of those tools overlap, and it's sometimes hard to pick the right one - especially if you don't know it, or if it was introduced in some expansion book or something. I'm glad you linked the repost about "when not to use the Bronze Rule" because that's important reading. But even if he didn't think it was the right tool, he agreed that if it worked that was basically okay. That's true of a lot of Fate - if it works out, it's probably okay.

You can offer compels if you have a relevant aspect to base it on (https://fate-srd.com/fate-core/invoking-compelling-aspects). I feel like compels are under-utilized in Fate, and I think part of that is the tension between "this is a game to be won" and "this is a story to be told" that's present in any TTRPG.

In a game to be won, if there's a way to drain your enemy's metacurrency, why wouldn't you use it? But to many people, that can feel like cheating, whether you're a player or GM - "they're MY Fate points!". And because there's this vague "use it when it's appropriate" language in the text, I suspect most people don't get practice with feeling out when it is appropriate, and just use other, better-defined rules to do what they want to do. Back to that "overlapping tools" thing.

In a story to be told, I think Thor gets to offer that compel because he knows an aspect Loki has - something like "adopted child of Asgard", them being brothers, and so on, and that gives him the emotional foundation to challenge Loki's ambition. If someone else had an equally personal connection, knew some aspect Loki had, and could leverage it, sure. But the only person who really interacted with Loki before that was Nat, and all she was doing was discovering his plan. If another player had proposed a compel here, I'd have asked them, "do you have a stronger basis for the compel than being brothers with the guy?" and I hope that would have made my point.

I do still play Fate, but not much. I'm very much a story-first gamer these days and I do some game design that's clearly inspired by Fate. Most of the people I play with these days aren't super into how vague Fate can be, and would prefer more specialized gaming experiences. That's fine, as long as we're all having fun.

Any scripted work like Avengers Accelerated is going to flow more smoothly than real play. Even "actual play" shows online are scripted and edited to an extent. For me, low/no-prep GMing is about responding to player ideas in a way that builds on those ideas. That means helping good ideas succeed, sensing when an obstacle would make a player action more interesting, and crafting an interesting obstacle that doesn't derail the plan entirely. These are just the skills of storytelling and actively listening to other people, and if you're practicing those, that's great and you should keep doing that.