They don't loosen as he's just standing there no, the elastic is pretty strong. They will start to open as you move the arms or the hands within the gauntlet. Then you have to futz with the gauntlet again to get the seams as close together as you can. They can be a pain I'll admit. If they'd made them clip click shut it would have been better but it doesn't detract from the figure for me.
A quick shot of how they pull apart with the elastic.
View attachment 417091
I might be in a minority but I think the cape is good as long as you don't mind it behind him. It's the right colour, length, and drapes really nicely. If you want to display him in the cloaked pose you need a custom, otherwise this one works well.
I want to have the full suit showing on this figure. I have the Enterbay for the cloaked look and can't imagine displaying both figures the same way.