All three of those run into some of the similar problems. Their action skill is a summon, but so much of their other stuff is combat based that I don’t see them falling into something that does have a permanent summon. I tried to reserve those for characters that were really about it - Gaige for instance gets her Artificer Homunculus (which is really oddly paired well to become deathtrap). Mordy gets Beastmaster because… well honestly people would lynch me if Bloodwing wasn’t a thing in that build - and they’d be right to because that bond is important to his character.
For the other three, I had to think a bit.
There’s a lot to be said in how Axton and Roland are similar, and both rely on a stationary “summon” to affect the battlefield and as stands, nothing else really mixes up the combat abilities and has something like that. So instead I focused on their other attributes. Roland for instance has a lot of support roles, but can still focus on offense. The first thing that came to mind for him (and I’m glad I stuck with it) is War Cleric because it fits his role of really supporting the team and being a leader without nixing any of his combat ability. This also has the added benefit of the main cleric “damage dealing” ability being Spiritual Weapon, which is a ghostly “summon” that attacks enemies as a bonus action at no concentration.
Axton… is different. He has much less of a support role than roland had, a bigger offensive focus, but played well he can still command the battlefield. In particular his capstones double damage with slag, deal a shitload of damage with nuke, or can control enemy positioning with tossing two turrets instead of one. To combine all that, I made him a battlemaster fighter. I haven’t got to set up his maneuvers yet, but my thoughts are trip attack (giving melee targets advantage on the target he knocks prone and does damage), and one of the swipes that controls enemy movement like pushing attack (which im too lazy to look up right now). He also has access to action surge which lets him attack more times a turn once a day, which again plays into his more offensive capabilities, and the other toys that fighter gets makes him an ideal tank if he needs to step up into that role, vis a vie his more defensive/selfish abilities.
Finally Willhelm, which was the real bitch out of these three. Even more than his action skill, willhelm to me screams customization. His entire character is built on slowly becoming less than man and more machine, and slow incremental upgrades to get to there. Yes, his claim to fame is a droid, but its not as defining a feature of again, say Mordy or Gaige. So to make him as “customizable” as I could with different options, I went with Simic Hybrid Warlock. I was really proud of this, because Simic Hybrid is a really unique class not seen a lot outside of Ravnica (I’d probably rename it something else, honestly). On its own that race can add any of several different features like gliding wings, crab claws, etc. Warlock also has its benefits in the form of spells learned, a forgiving spell cooldown in pact magic, and most importantly “Invocations”, which I see as slow upgrades that willhem does to himself as the game progresses. I chose Hexblade because it feels like a lot of charcters like him will be pushed into more melee trees, and hexblade allows for a few different interesting playstyles. I went pact of the chain because it gives him a psuedo-permanant “familiar” which can play the role of at least one of the drones. Finally, the whole theme of a warlock making a deal with a being bigger than itself for power is Willhelms entire arc. It fits the character too much to ignore. In the end, he probably won’t be the best sheet I make out of the mix, but after the thought I put in this morning I think he might be the best flavor wise, on paper, for DND.