The solution should be any MP function should allow for a "solo mode" so no content is missed for wanting to play the game by yourself.
That might work nicely, so long as you could take SP squadmates to help out. Some of the MP objectives can be difficult to complete by yourself.
You only needed to play a couple of MP matches to get the "breath" scene.
"hundreds of MP matches" is either an insane exaggeration, or the only person at fault is you for playing far more matches than was actually needed to even hit 100% readiness.
That kind of depends on the luck of the draw, doesn't it?
First, there's a learning curve to figure out what is expected and what are the best strategies for MP. Then, you need to keep your fingers crossed and hope to land in a group that will make it to extraction, or at least complete some objective(s) before wipeout.
For any SP content to require success in MP automatically makes you dependent on other players - sometimes complete strangers - to achieve your goals for SP. Yeah, I realize some people are good enough to solo, but MP is designed for multiple players to work together to be successful. Requiring people whose only real interest is to unlock SP content to achieve that level of performance isn't going to give your game mass appeal.