Ackles deserves a story arc that remains his, that gives him some decent material to get his teeth into, and that progresses his character rather than regresses it.
Summed up beautifully, Observe
. I'm so tired of the hamster wheel Dean's been on. Ackles does his damnedest to keep life and spark in it but it has to be disheartening to see your hard work squandered all the time. It's time to move Dean forward and progress his character, not deconstruct it, not regress it, not try to make someone else "the new Dean" while giving the "old Dean" nothing to do but stand by and watch. Dean is all the Dean the show needs and he's been, imo, brilliantly portrayed by Ackles for 7 years now. Give it some payoff instead of a treatmill.
Let Dean be the protagonist in his own storyline, let his experiences mean something, let them allow him to bring something useful to the table in the overall storyline. Something other than "oh you're weak, you're pathetic, you're just a human, you're replaceable in this story".
This is a great opportunity to showcase Dean's innate intelligence and creativity and make it essential to their survival in Purgatory. People sometimes pay a bit of lipservice to "booksmarts and streetsmarts of equal" but mostly on this show - the writers simply get lazy have everything findable in a book of some sort. Something someone else has already written down, already discovered. And normally it's someone else who researches it and finds it(Bobby, Sam, though Dean's capable of doing research too).
This is a chance to put their money where their mouth is and show "streetsmarts"(creative intelligence, the ability to learn on the fly and quickly) is truly just as respected someone who knows how to crack open a book.
We've seen enough of Dean over the years, IMO, to see that he is really a very intelligent man and it's a complex intelligence as well. He's great at thinking on his feet, he learns quickly, he's creative in how he uses what he learns, he knows how to put other people's abilities to good use(which is one the things that makes him a good leader), he's got great instincts, which is really just another way of saying he internalizes what he's already learned well, he's good at reading situations because he's observant--often even when it doesn't look like he was paying attention. He's clever.
He has his own areas of expertise - like he seems to know a good deal about how plants are used in spells and magic.
Dean also seems to be a real whiz when it comes to some spells - there has been at least twice on the show where Dean's seen something done once, done in a real hurry and he's been able to exactly recall the writing or ingredients to re-create the spell(Ep 5.1 and The French Mistake are what I recall off the top of my head). He's good at recognizing patterns and symbols.
He's got good mechanical and technical abilities - he built an EMF meter, he's the one who decided they should use salt shot gun shells(see Hookman - Sam is surprised to see salt shotgun shells, apparently they didn't use them when he was around, Dean implies it was his idea--he didn't invent them, I've heard that farmers and such often use them to scare animals away but John apparently didn't use them when Dean and Sam were growing up until after Sam left for college), he built an EMF "bomb"(Ghostfacers), he can rebuild a car, he can disarm some pretty advanced security systems.
Now the electronics probably won't be a problem in Purgatory. :D But the idea behind the skills are transferable. If he could figure out how to do all that stuff, he can figure out how the world works in Purgatory as well and come up with ways to use what's around them to try to defend themselves. I don't know what kind of plant life is in Purgatory but there is some sort of plant life there - which means something might be useful at some point against some creature. He, with Castiel's help assuming Castiel remains there, should be able to come up with ways to survive.
Sometimes I think one of Dean's biggest problems has been that he doesn't think of himself as intelligent so he just assumes someone "smart" will know better on certain things. Aside from the occasional doubts, he basically trusts his instincts but he doesn't necessarily trust his actual knowledge.
Like that episode I think it was called War What Is It Good For(5.2?) - that was great example. Dean knew the answer but Ellen almost had to point it out to him and I loved her for recognizing it like she did. He knew, he'd read the Bible passages and once she said essentially "Think for a second, you can figure this out, you don't need to call Bobby or Sam" and he did--he knew how to apply what he'd read in abstract way to the situation at hand. I remember, in that scene, feeling really good for him.