What’s a lease line?
At a technical level, the Now signal will not compensate for any shortcomings in the transmission to your equipment by dropping to 480p; it will pixelate or buffer. So if you are getting a steady 480p, you need to determine what your PC is doing to drop the incoming 720p to this lower resolution.
But how do you know the spec of the Now video picture you are getting on your PC? i.e. where are you reading off 480p?
What is the video spec of your PC? What is the make and model of your PC?
But as @redchiz1 mentioned, Now on a PC is not its best self (too many variables in the receiving platform to contend with) and you should not condemn it without seeing it as it was intended, via a Stick/box or as a native TV app.
A lease line is a business level internet connection. 400mbs up and down at all times , I mention it because the problem is exactly that They sell the subscription to pc users knowing full well how bad the video codec is for the pc app , it’s not about using a tv only . A steaming service that has its worst service at the pc level is just baffling . At least state this issue when selling the product . Either way I’ve cancelled and will never pay for a service that just does not deliver