While I don't think you're wrong about how a 3 year interval would have been terrible, it's worth noting the environment these films would have been released. Movies aren't released in a vacuum, which is why the complaint of the MCU having become stale could only be made now rather than a few years ago. 2014 was a banner year for the MCU with GotG and Winter Soldier but by the time AoU and Ant-Man came out in 2015, people wanted something fresh instead of something familiar. Back during phase 1, movies like Thor, First Avenger, and, to a much lesser degree, Iron Man 2 still felt somewhat new and fresh which greatly benefited their reception, as did the short intervals between each installment like you pointed out.
But even with all that in mind, it's a bit off to suggest that the consensus for phase 1 is that it's a mediocre product or even a homogenized product. We've had dozens of comicbook movie ranking threads and in every one, you'll find a wide range of opinions for all of them except IM2 and Incredible Hulk which only have a handful of fans.
We've come to the point where we have an embarrassment of riches as far as comic book movies go. For that reason alone, we're going to see all projects receive a lot more scrutiny from here on out. Heck, I'd argue the heightened scrutiny began last year. Standards are only going to get higher.
