The caravan isn't as bad as people say in icing - but you have to get out of the ice, you cannot linger. That's pretty much all there is to it. To be fair i never flew a 600SHP van in icing, but I flew the 675 van in icing in the PacNW and some up north here, and I flew the EX quite a bit too. Lots of the terrible performance basically went away as soon as they put bigger engines on it or TKS, or both.
The problem I remember in the 675SHP van was that it's easy to be doing your paperwork or something and look up and suddenly you've lost 10kts. In the 675 they were really sensitive to where the ice was iirc, and the airspeed could be trending down before you realized you were even in icing. I felt like the airplane really came into it's own with more power. Having flown the Aerotwin Van and the EX I'd say that it's a demonstrably more capable airplane with more "oomph."
The EX is really performant and great, the only disadvantage is that you can run out of TKS, but you don't insta-die when that happens, it is just an emergency and things get a little more exciting. Still, the one time that happened to me there were plenty of options and it eventually worked out fine, the key was doing all that route planning stuff you're supposed to do before flying anyway, so I had options. Things could have gone very differently had I not planned.
I guess my take on the van is "it's fine, it's good enough, it does fine in ice if you actually follow the requirements of the AFM, but requires respect", more than say, a Navajo, or a Baron a lot more. The crazy thing about the Navajo was that it basically didn't care about ice - you be slinging scary amounts of ice off the prop making some helacious racket and beating the crap out of the nose baggage and literally no airspeed was lost. You'd see ice forming on the VGs of the BLR kit at max gross and literally not even worry about it. Meanwhile in the 675 van a snowflake hits the wing and you're 10 kts slower.