The games my group has gone through seems similarly themed. Currently the game that might fit the bill is far, far west. Similar gameplay to helldivers but dramatically more forgiving and easy to complete runs in 15-20 minutes or spend more than an hour scouring a map.
I personally have been absolutely loving jump space. No classes per se, but flexibility to choose your load out with variable gameplay and relative forgiveness in missions. It’s still early access and I’m just very excited for its future.
Other games we have enjoyed at length that might fit some of your listed interests:
Risk of rain 2 - tactical 3rd person fps
Gunfire reborn - tactical fps rogue like
Deep rock galactic - tactical fps
Inkbound - turn-based
Slay the spire - deck builder
Vellum - similar to gunfire and risk of rain but with a book/literary theme similar to inkbound
The ascent - not rogue like, but top-down action shooter
Gatekeeper - isometric/top down shooter with a similar feel/theme to risk of rain 2
Trine - not really an RPG, but it has classes and you have to cooperatively solve puzzles
Far, far west has been more enjoyable for our group and scratches the itch left by helldivers. We have similar skill gaps and with the variety of weapons and spells, any player can still feel like they’re contributing. Plus death is not as punishing; there’s no maximum respawn and you can still move and attack while you’re dead! This also allows you to run to your teammates for a revive.
Gunfire has multiple classes to pick from and I feel is similarly forgiving. I will say that the early game might feel like a bit of a grind as you work to have enough in-game currency to unlock things.
Once that is done, the variety of choices during a run allow each player to work toward mechanic and while there is synergy between some classes and builds, the game does not punish you for NOT pursuing those. So it isn’t crunchy tactical like xcom might be, but it still requires coordination at higher difficulty levels.
I have about 500 hours played in gunfire and they continue to have engaged road maps and interesting DLC that keeps me coming back.
Would agree about StS2. Our group had a bunch of fun while we each tried the different classes. Now that we have most of the content unlocked, we stopped playing to wait for the final release.
Hope that your group jives with some of these and have fun gaming!