I mean, Dueling is relevant but it doesn't show if you have teamwork etc. Dueling will only be relevant in 2v2's, 3v3's and maybe 5v5 tourneys.
Dueling gives a pretty good idea how well someone understands the mechanics of the game and how well they can apply them.
Groupfighting shows how well you can work with others and handle a variety of different circumstances (like being outnumbered).
They each have criteria that are necessary for judging a players skill, and to pretend one is more important than the other (not saying you're saying this, just in general) is ridiculous.
I hope it's clear I mean duel tournaments and random FT7s, not within a small GF match context. Winning duels within a GF is the least consistent way of ensuring a win, but yes it does count for some sort of time-pressed raw skill. However within duel tournaments or whatever, it is the most one-dimensional style of a patience contest, and doesn't really indicate anything since you have no other circumstances or context to the fight.
That entirely depends on who you fight. Yes sometimes it is just a match of patience and in that case, yes it can be disregarded as a skill indicator. But from my own dueling experience (mostly on NA, but some EU too) that's rarely the case, and it's mostly just a select few individuals who hardcore s-key and do other desperate tactics like that to drag it out and turn it into a patience match.