72 ppi is a curse from the evil ancient spirits of archaic computers! 72 ppi begone!
Normal computers are closer to 96ppi
Yes. Let me do some math for you.
For example a 14" laptop screen will have:
But at 1280x720 will be
Another example, a 23" monitor will have:
1. Make a decision on what is the final pixel size you really need. Pixel in px units... forget the inches " physical units. Xo)
2. Play with the settings on whatever you have on your InDesign file to export at that final pixel size.
3. Although 72ppi has no sense, still, the applications use it, so probably 72ppi will export the asset at the dimension you intended to. Do what Lucian proposed in his answer. Export at 2x.