Some meandering thoughts, and a couple questions…
Happy to help
And he’s very helpful, but not necessary.
But in general, Guardians is the first place I’d prioritize Summoning, because Jackal and Falcon are hugely helpful for Titans and Offense — and as 4*, they’re actually moderately obtainable.
I typically recommend that C2P players Summon only on Guardians amongst the Challenge Events, until getting Falcon and/or Jackal.
If you Summon and get lucky enough to get Falcon, then he’s well worth power leveling — presuming your bench is otherwise well established — which may not be the case from your list of usable heroes.
In your case you’re probably better off sticking to a rainbow leveling plan for now, to build bench depth.
Mono isn’t necessary, it’s just easier.
But the value of Falcon is most increased when paired with strong red attackers. Gormek adds little value there, since Wilbur covers defense debuff, and Gormek and Sumitomo both have low attack stats.
So I wouldn’t recommend prioritizing them for Challenge Events — though they’re useful heroes elsewhere.
It’s definitely achievable without mono, and without a ton of Emblems. I’ve seen others rank moderately well with other team constructions.
Using Wu is out for Guardians (or at least is fairly risky), which undermines one way people avoid mono.
In your case it sounds like you almost don’t have much choice other than a 3-2 stack of Boldtusk/Wilbur/Kelile, and 2 of Proteus/Ameonna/Tiburtus.
That’s actually not a bad team, and has some good damage output potential. You’ll likely just need more Battle Items to finish off Bosses than you would with more hitters.
How’s your inventory?
You’ll have your best potential runs in Stages where the Bosses are green or yellow, and you can charge (or Mana up) Boldtusk, Wilbur, and Ameonna as needed to bump up damage quickly on the monsters or Bosses. You’ll likely need to finish off some of them with Battle Items too.
You might be a better speed player than me, but it took me a while to get decent at playing quickly through Stages. (I’m still nowhere near as good at it as a lot of other people, I only got good enough to hit the Reward Tiers I wanted.)
So I’m also wondering how much you’ve practiced that on past Events. You’ll have to work harder at it because you don’t have the added advantage of a mono team, plus you don’t have a lot of hitters, so damage output will be lower.
I like to practice while farming, so you could try that too if you haven’t been already.
So in upshot, just trying to figure out a little more context of where you’re at with Challenge Events, to figure out where to focus your attention.