The size of the shields alone aren't that high actually, but the damage penalty smaller ships suffer make them pretty awesome.
Python rocks!
I don’t mean to be picky, but I think the smaller weapons penalty doesn’t apply to shield damage, only to hull.
To OP. It’s sounds like a lot of exaggeration to be honest. The Python is a great ship. As others have said, a D rated power plant is probably an issue. For heat issues you are much better off with A rated, but you don’t have to have a size 7 power plant. You can run a size 6A or even a 5A for a trader outfitting. Can you post your full outfitting on edshipyard or something. I really don’t think there has been a nerf with 1.3 for any ship.