What was the build lol. Well done and thanks for the kind words - did you feel like the difficulty should have scaled more?
Hard to say, I feel like the new update made things more difficult than ever, I just got REALLY lucky. Like after the last update I was slightly demoralized momentarily because it took me so long to get three stars on the campaign mode, to the point I still haven't got three stars in a couple of maps.
This is the last screenshot I took from the game, a few waves before it ended. 
All in on range and the slowing effects of ice, range was big enough so that the sniper classes covered the entire field with ease, and like 95% of the map was covered in Ice, and I had a ton of extra perks to increase the slowing effect.
(Worth noting is also that I had tons of 200% damage increases on physical attacks, and so many extra projectiles, extra targets and pierce bonuses, that the game was slowed to a crawl. I was at like 5 fps at the end, and worried that the browser would crash before the game ends.)
And this was my loadout when I started. The only major difference in the characters seen on the other picture is that I had three star miners for the majority of the game, but nearing level 50 I was so close to failing that I switched them out for more damage and wound up selling them later. So I was all in on economy in the beginning and did fairly well thanks to it, but I feel like in the end it was just that all the stars aligned, ie. it was down to luck more so than any single thing being so broken that they hard carried me. Or that's what it felt like, I'm sure you can deduce more than I just based on these pics alone.
A final addition two days later: I was able to do it again with pretty much the same setup, on the same map. Range, burn, ice, poison, stun, fear and damage amplifications seem to all play a key role. Especially the 10% damage amplifications when stacked seemed to do wonders. The enemies slow to a crawl with multiple slowing effects all stacked, and on top of that, high stun and fear chances etc.
Highest damage dealers were as follows:
Bashful's damage +24000 M, Sleepy's at +16 000 M, Ice at +7600 M, Poison at +6000 M and then at fifth, Stormivan at <2000M.
I think that Bashful and Sleepy are both incredibly powerful even on their own right, but it's also that they both were in range of the first straight on the map, during which all the fear and stun effects procced, so they easily had much more time to deal damage than most of the others. But even so, the difference between Bashful's damage and that of the third actual character was more than 10x.