I agree with you. I had a similar experience with a K frame model 19 purchased new in 1964. I fired nothing but full house .357 mag shells in it. After shooting only 200 rounds the gun got so hot the cylinder would bind.
You sure it wasn't just lead and carbon build-up on the cylinder face/forcing cone? A '64 K-frame was a hand-fitted, P&R gun with tight tolerances.
I had a P&R 19-4, didn't shoot it all that much before trading it for a 1966 Dodge Pick-up, but it ran fine with mag loads. My M65 has also seen plenty with no ill effects, as has my sister's 65LS.
With a 686 and 586 on hand, I don't typically punish
myself with hot loads in the small, light K-frame these days when I have larger framed guns that make it more comfortable. But I also don't hesitate to load K's with such ammo if I want to carry something lighter & slimmer.
The N frame is the most rugged and the 686 is a very good compromise
The L-frame is no compromise; The very heavy cylinder of the N-frame in .357 causes them to batter the stops with rapid DA firing. The L-frame was designed to handle any .357 load without being unnecessarily large and heavy, a task that it excels at. The L is a very robust firearm.
As to the original topic, old as this thread is, I'll offer my take:
The 686/586 are known as the "poor man's Python" or "working man's Python" for a reason. I like Colts just fine, but when I can buy a nice pre-lock L-frame for 1/3 the price that shoots just as well and is a simpler, more robust firearm (albeit not quite as pretty), it's simple math. In point of fact, given the choice between the two and not incorporating price, I'd still take the L frame.
I also have never cared for Colt's backward cylinder release. It's just counter-intuitive.
However, owning 2 L's already, if I saw a Python and a 586 in the case for similar money, I'd grab the Python. That won't happen, of course, but just sayin'.....