The issue is that if you cannot take off yourself, you cannot abort a landing.

So if you have to keep it, you're trading a bit of efficiency for a lot of complexity.

The tug could be more like a powerbank. It would not physically pull the aircraft up but assist by providing power. The aircraft could launch on its own but it is advantageous to use a tug because this increases the range or energy reserves that the aircraft itself has.

(outline of a launch: aircraft and tug are connected by cable before launch, both lift-off, gain altitude, cable is detached, aircraft moves on and tug returns to launch site)

Except you probably have another aircraft already landing, the slots are tight. Maybe you could have another shorter landing strip just for the tug, but again, that seems like a lot of complexity (i.e risk) for maybe a 20% increase in efficiency at best.

Like in the other comment in this subthread, I had vertical take-off and landing vehicles in mind.

You can even ground tow to altitude then go flying.. Glider have been doing that for ages..