Group fly does work well, just provide that your flyspeed isn't quicker than your henchmen. Henchmen flyspeed is inherently quicker than ours (32mph compared to 24mph for us) so even with the likes of swift enhanced with flyspeed, your henchmen should be able to catch up. the slower your flyspeed the better. they may tend to lag behind, that is due to the server lag and whatnot, and there's not alot you can do about that unfortunately.
I'm playing as a storm with Steamy Mist, which is great for stealthing my way through open areas to get between missions, but.... my henchmen never keep up. I can't go anywhere without them drawing trouble, even if I tell them to heel. They trail too far behind and don't get the stealth on them.
So, I'm wondering, if I took Group Fly, would that solve my problem? Or would they still trail behind, and get seen, or fall (because of getting out of the Group Fly radius), and keep causing me trouble. It's not really worth a power selection if it's not going to solve that for me. Not like I would want to use it in combat or on teams. (Though it makes wonderful thematic sense for a person who controls the weather to be able to make others fly with them.)
At this point, the only working solution is to just unsummon them, and resummon when I get where I'm going.