The problem is that he was a "Forever DM" for years until he joined this game less than a year ago.I think you mentioned there's at least one other old timer in your group.
We will be losing a couple players to college this fall, so I think the group will condense to a more manageable size for me. That would probably be a good time to see if we could get some boardgames playing, try out a new system, etc.
For whatever reason, when I run it (whether with a group of 7 or 4), around 5th level it turns into "superheroic" action. I just can't seem to figure out how to challenge those characters.Interesting. I think 5e is default heroic action and you actively have to work to make it something else.
When you're dropping some of the highest level opponents the game has to offer at a 7th level party to make it a tense fight, where do you go from there?
That requires a very delicate balance. And apparently there's a "magic formula" WotC is keeping secret for encounter design - which is frustrating.Also, I really started to enjoy DMing more when I started to prepare less. I know this isn't your typical style (and it wasn't mine), but I suggest you try to embrace improvisation more. It can be hard, it was for me, if you are not used to it. But it is incredibly liberating when you embrace it. I don't really need to prepare monsters and encounters anymore - I can run them on the fly with my DM cheat sheet / screen, which, with the exception of our house rules, is RAW from the DMG.
But I suspect if I just pulled out monsters I thought "looked cool" it would be a jumbled mess of simple fights and an unexpected TPK here and there. And without planning and strategizing, I wouldn't be using any of the monsters to their fullest potential.
And I'm sure story, setting, and all those other intangibles would suffer. I would forget to give treasure - or give too much, which was the disaster of my previous game.