As far as I can know, Mackie's a good guy, but he's definitely a supporting-character level of actor. There's absolutely nothing wrong with that, either: he bounced off Cap and Winter Soldier very well every time they were on-screen together.
As for Falcon the character, he deserved a stint at being Cap as much as Bucky and others have in other adaptions and comics themselves and he got a genuinely snazzy-looking Cap costume. But the issue is like when Nightwing becomes Batman or whatever: Cap is Cap and Falcon ultimately isn't, he's the Falcon. The only time a successor in superhero media truly succeeded to the mantle was Wally West becoming Flash, and that took both years upon years of hard work and quality storytelling in the comics, and plenty of characterization in the top-tier DCAU, to pull off.