The bolded words are what I have an issue with in your post. For once in the last 10 years every single route in the game works. Deep comebacks, corner routes, the C routes, dig routes, drags, slants, speed outs, quick ins, short hitches, curls, whip routes, sail routes, posts, etc. all work.
Now its true that slants are the most effective route against man but with a good route running WR you can burn man coverage using deep outs, dig routes, whip routes, and many others. Concepts like mesh and shallow cross are designed to put a lot of stress on man coverage (as well as zone) as is something simple like Z-Spot from a bunch formation. The spot route is pretty hard to cover in man coverage as long as you have the timing down.
With routes like the Corner in Z-Spot or the deep corner routes (c routes) in the Corner strike plays you can actually throw your WR open if you have a decent QB. You can do it with less than adequate QB's (did it for 2 years with a below average Kolb in online franchises) but its obviously going to be less consistent but you'll usually just throw that route out of bounds instead of throwing a pick since it is an out breaking route.
One of my favorite things to do with Green Bay (my favorite team and thus the team I play the most with) when I go up against someone who plays a ton of man coverage is to first soften them up by running a lot of short quick hitting passing concepts such as slants (its not like any sim player would ban them), shallow cross, Drive, Mesh, Z-Spot, and spacing (preferably if you catch them in zone after all the short middle passes). This forces them to abandon the 2 deep safety look to play some sort of robber coverage if they want to stay in man coverage which lets me open up the offense and go for the kill. Once I notice them in either cover 0 or cover 1 on multiple occasions I'll try to isolate either Jennings or Nelson with one of GB's trips formations or their Gun Bunch formation and run a play that has one of those deep corner routes (the c routes). If I have decent protection I can make a throw with Rodgers that will be just about impossible for the defense to get too and normally if they go for the pick they'll miss leading too a big play for the offense. They are forced to take the conservative play and attempt to swat the ball or knock it loose after I go for the catch and while this seems really easy way to slow it down or stop it many people try and go for the pick and are often found trying to run down Jennings and Nelson as they break up field.
If they start laying back and not going for the pick then you can start throwing in deep comebacks and rarely have to risk throwing a pick. You can do similar things using deep outs out of passing concepts like Strong Flood as you throw a bullet down and towards the sideline allowing you to come back for the ball near the sideline while making it almost impossible for it to be picked off by a defender in man coverage as long as WR is a decent route runner.