You're overrating De Gea a tad bit much. Edwin was a beast who rarely ever made a mistake and was a wall in front of the goal. Sure, he didn't make as much flashy saves as De Gea has (which is probably why you overrate De Gea), but his positioning, awareness and defense control is miles ahead of De Gea's.
Agree with Edwin not being flashy. Edwin had that quality where he'd be so well positioned most of the time that he didn't have to resort to insane flying save. He made goalkeeping look easy thereby never got same level of praises as some of his peers did.
I don't know who is better between Edwin and DDG though, their styles are so different that comparison is very difficult.
Now that I think about it, current CB suits Edwin more whereas Edwin's CB would have been better for DDG. Right now we don't have really have a defacto leader at the back, our CBs are rather inexperienced and somewhat weak in air. Edwin could have been more suited for current crop with his, as you said, defensive control, positioning, aerial presence .
DDG would have been better behind peak Vidic and Ferdinand, those guys were natural leaders and would be able to protect DDG in set-piece scenario, which is DDG's weakest area (mind you, he is still excellent, just that he is much better at shot stopping, then coming off line and dealing with set-piece deliveries).