It's not a fair way to compare.
- The sales that the Wii had are the most important reason that all the Nintendo games made ridiculous numbers.
- 3ds & Wii U Smash came with no competition to both markets (3ds also beeing THE device in Japan).
- SFIV came in when fighting games were almost dead (mainstream). Also in a ridiculous time with Batman, ACII, CoD:MW2, Resident Evil 5, Uncharted 2, Bonderlands, Left 4 Dead 2, Dragon Age Origin.
- Don't think I have to say what happened with SFIII and the time it was.
- SF still sold 7M (according to Capcom) besides the fact that was bigger in the arcades
The problem with SF it's that it's not a party game like smash. I'm sure everybody has a friend that likes the game but doesn't buy it cuz "I suck at FG". Not saying it could surpass Smash in sales, but if it was as easy to play for casuals I'm sure it'll be much closer. Let's see how SFV does in the long term.
I like how your first two points are taking different sides. Brawl sold well because the Wii sold well! Ignore that Smash 4 is selling well despite the WiiU selling terribly, because other reasons!
Then there's the fact that SFIV had so many versions and platforms to sell on, which makes your third point contradict the first two. If we posit it against your second point, SFIV had no competition in its market, so it invalidates itself again.