De Gea is world class and anyone who doubts it is a bit foolish but thats not really the issue. He is indeed average with his feet, and so is Hart (hart is also seemingly extremely weak on his left side with shots soo by the way), but the difference is DDG has Mourinho as his manager, Hart has Pep Guardiola.
The main difference being Mourinho will probably use Valencia as a right back and have DDG pumping balls anywhere near the right side on the half way line for him to head on, like he did with Cech and Ivanovic at Chelsea. It was an abysmally dull tactic but one they used as option 1 when Cech had the ball. Efficiency with his feet doesnt isnt relied upon under his prior or present manager, so his world class talents in shot stopping are the most forthright thing about him.
Now, Hart is about to be coached by the absolute professor when it comes to playing out from the back. Whether he is as good a shot stopper as DDG isnt important (unfortunately he isnt, despite immense potential and world class performances in some games of course), what is important is whether he is as good with his feet as any keeper potentially in the market. Bravo and Ter Stegan are excellent with their distribution, as were Valdes & Nueur for Pep.
People talk a lot about Oh well I am more arsed about their shot stopping, and I concur to a point but Pep is used to his side being hugely dominant in games where the keeper is often only used probably for the ball at his feet or claiming crosses/corners from some counters etc. I know it is different here in the Prem, but judging by the very first pep session being all about playing from the keeper and at the back, and with Stones incoming; I really dont see much of a future for Hart.
I do expect him to get this year to prove himself, purely because I dont see any real news other than some twitter rumours right now..