[duskwuff]

> And as the departing plane goes faster, doesn't the lift take stress off the runway?

Only for a short period between rotation and liftoff. Most of the takeoff roll is spent building up horizontal speed; the pilot doesn't command the aircraft to pitch up before it's ready to lift off.

[absurddoctor]

There will be lift almost as soon as the plane begins moving forward, reducing the weight of the plane, which would seem to reduce downward stress.

[ExoticPearTree]

You are half-right. Actually pilots push the stick forward to force the plane to stay on the ground until it reaches takeoff speed. If the plane would rotate naturally because od the air passing under the wings it would generate a lot of drag.