I define a blockbuster the same way everyone else on the planet does.... when the film is so popular they are lined up around the block.. thus the term.
The Avengers is a blockbuster, the Proposal is a film that did relatively well. Making millions isn't all that impressive these days... we are in the era of mega movies.
He's starred in a lot of big budget bombs and/or critical failures. RIPD, Green Lantern, Wolverine.
Everyone on the planet? Interesting. Vocabulary.com defines blockbuster as "A blockbuster is a Hollywood movie that's made with a large budget and big stars." Dictionary.com is "a motion picture, novel, etc., especially one lavishly produced, that has or is expected to have wide popular appeal or financial success. " The common thread for the term is high budget and high expectations. Waterworld was a blockbuster, for example, one that tanked. Green Lantern would be another high budget movie with high expectations. These days the term is slapped on any big budget summer movie that is expected to do really well. But it originated as a name for a big bomb (one that could blow up a block, hence blockbuster) and in the 50's became theater slang for a play that lines people up around the block. I don't think it actually started applying to movies until the 80's. And "blockbuster" movies only cover 1-2 movies each year, which accounts for a tiny fraction of total Hollywood revenues and represents a small handful of A-list actors. Blockbuster movies are a huge risk to studios, so while they might be the most memorable when they do well, they are far from the norm, and definitely not the thing that drives Hollywood.
RR has starred in some big budget movies, and yes, most flopped. But in the rom-com genre, The Proposal is the best selling movie of all time. He was one of the most wanted actors in Hollywood after that, but then he did Green Lantern and it propelled him back to the mid-list. In other words, this isn't his first time at the top. So when a bunch of people post about how his greatest film ever is Van Wilder and how he has never been in a top end movie, I wonder what rock these people have been hiding under.
Then I realized it: You guys aren't big movie goers (or maybe the right term is movie-lovers). You see movies that make the news, that you hear about from friends, or that are very specific to your interests. So of course since he hasn't been in those 1 or 2 movies each year that really blow up and are all the buzz (of the hundreds that are made each year and are profitable), it would make sense that RR is seen as some nobody.
I go to ~40 movies per year at the theater. I watch another 200+ movies at home throughout a year. I see just about everything that piques my interest, which covers just about everything outside of Horror films, and in the last decade, several have starred Ryan Reynolds... several moderate to large budget movies, in fact. If I am seeing this guy over and over in mainstream movies, often in leading roles, then in my mind he is a top actor. But yeah, to a non-movie goer who only acknowledges that a couple good movies are made each year, I can understand the point of view. It is all a matter of perspective.
Personally, I think he is a decent actor, not great. He can do drama just fine, and of course comedy is his strongest point. He was well suited for Deadpool.