I've never seen someone hold a formal strategy brief at the start of a dungeon in about 10 years of playing. That sounds on par with trying to organize a Sastasha clear where you make voice chat mandatory to discuss strats.

You're much more likely to see idle banter when you have players sitting around waiting for something to happen. That can happen in dungeons if someone disconnects, but it's more common when you're waiting for a PF to fill or doing larger group content in a big zone (hunts, FATES, Bozja CEs, etc.) Dungeons are fairly streamlined and designed for players to be able to get in and out quickly even if they have limited time to play on that day. So you'll find that a lot of people aren't there specifically to socialize, because they're mentally expecting to be in and out in around 10-15 minutes.

It's unnecessary. You can communicate everything that you want through movement alone. If you only want to do a partial pull as a tank for some reason, then you hit sprint from the outset to pull fast and decisively to your chosen endpoint and hard stop there to communicate your wishes. If you want to do a full pull as a DPS or healer, you follow one pixel behind the tank up until the first pack and then hit sprint past them until you're standing just before the activation point for the second pack. There is no 'leader' role. The person who leads is the most decisive person present. And if you don't issue demands in chat, then you won't have an argument about it, either.

This is a complete non-issue.