The tradeoffs inherent to the physics of optics are usually mitigated by increasing the size of elements across the axis, added elements, better coatings, etc. A major tradeoff is mass. For many brands a 50/2 is almost 30% less weight than a 50/1.4, and usually less than half the price, with both having near equal sharpness and distortion at f/2.8.
Originally Posted by Rol_Lei Nut
I had a Zeiss 50 for my Pentax system. It had superb center sharpness and resolution and great colour rendering. Its edge distortions were noticeable until 2 stops down from max. It was also worth 2.5x more than a Pentax brand equivalent but in real life photos, it was hard to see the differences. It had great all around performance, but there was a flaw based on the unavoidable optical physics limitations. I could get the same performance out of much less expensive glass at the expense of 1-stop.
I therefore concluded biggest discrepancy is price vs. noticeable distortion in real life photos.