I figured it out

There’s some good challenges there. I got bored trying to find them though, going back through the levels is a bit of a chore.

Got back into this (finally). Up to world 3.

Just two bug bears so far: the frequent sections of the game that won't let you rotate the camera, and Luigi. Is it just me, or is he borderline useless? He's one of the first characters to be introduced, but I've only found a use for him in world 3 as the maps finally open up enough to make use of his long range fire power. And then the enemies gain the ability to teleport, so you can't stuff him on some high ground and expect him to stay safe. Rabbid Peach is basically a must to act as nurse maid, her healing ability acting as soft counter for Luigi's ridiculously low health.

The game mechanics themselves are almost a hard counter for Luigi. What use is high mobility and long range weaponry when you and your enemies can team jump, often multiple times for a single character? On a recent map on which he'd technically be perfect (the heroes have the high ground and the enemies are stuck* on the low), the opposing Rabbids with grenades made mince meat out of him. I restarted the battle, chose Rabbid Mario and Peach, as one could use their shotgun-style weapon destroy cover, and then exposed enemies can often be one-shotted by the other's fire.

Am I "doin it rong" or is Luigi a bit pointless?

*Stuck bar the ones that can teleport, natch.

I've found Luigi useful so far. Good for setting up one turn kills.

Yep.  It's not locked in when you upgrade your stats, you can just remove and rejig.  Very handy/clever way to give the player a helping hand if they're struggling on a certain mission and need to beef up a particular attribute.  I'd dropped Luigi by the final third (I did bring him back for one stage near the end iirc), but he was a big player early on.  Rabbid Luigi can tear up certain maps though.  Rabbid Peach was probably my least used character.  Nice to know the game works well depending on your play style.

I use Rabbid Peach a lot, she's got reasonable offence and her healing is super useful. Plus I like activating her shield and then sending her out to trigger people's overwatch. Teaming her up with Actual Peach is a combo I like; it's similar to playing a White deck in Magic the Gathering. "OK, I deal you ten damage." "I heal eleven." "FUCK."

I used to use Rabbid Luigi a ton, especially after he gets his vampirism skills. (Which is ever so slightly sinister.) He's a damage monster, but I've found that since I've got Rabbid Mario and Peach, they can do pretty much the same damage but from range. (And often to multiple enemies, as they have 'shotguns'.)

I'll definitely remember the Orb rejig, that'll be stupidly useful.

Normal luigi can do massive damage if I recall correctly. He's a sniper, chuck him at the back with his 3/4x overwatch shots and he is very useful. Also his little bomb thing is good for getting rid of enemy overwatch shots and also hits hard.

Plus I think he has great movement for those missions where you need to hoof it across the map

Rattling through the Donkey Kong DLC. Great stuff, but one of the glitchiest games I've ever played. So far I've been kicked out of the software completely, had to reload story scenes/battle intros that didn't progress, got stuck in scenery and managed to glitch a block puzzle that is now permanently stuck in place. Reloading doesnt reset the positions - two blocks resting against each other that now can't be moved in any direction - and it's the fourth part of a long puzzle section (find four chests to open a fifth) that would've given me something useful. I've now binned the block push bits completely because I'd done the lot up to that point and it's pissed me off.

Everything to do with the battle system and new additions is brilliant, but from my experience it could do with a bit of a tidy up with a patch.