This is a bad assumption that you can disprove for yourself in 10 seconds. You aren't pushing air up a slope you are creating a pressure differential. An impediment ought to at best result in a small decrease in the speed of filling and a tiny amount at that because your mask is very porous. Your mask is effective not in proportion to keeping air out but because larger items like globs of spit get stuck on it and because of electrostatic charge.

There is absolutely no reason to believe that effectiveness at preventing infection is linearly correlated with difficulty breathing or that to a degree that the additional friction induces difficulty must rise to the level of preventing breath in order to be effective. You aren't preventing 50% of particulates from getting in by preventing 50% of oxygen for example.

For example I imagine that you didn't believe that doctors wearing masks pre pandemic or construction workers weren't just going without breathing well for hours given paucity of air becomes an problem very very quickly