From: Beijing, China
Unfortunately, you are talking from ignorance....have a look @ the games by CHOAS45 & Pelton ( although PeLton games may have been scrubbed for being naughty).
These 2 players would regularly Take Leningrad by turn 7.
Of course i am only commenting based on my own experience (who doesn't?), which is just a few months at most. But still,
1. The two players you mentioned are in the past time. I only heard of Pelton. Player skills never ceased increasing and the game updating, so their experience might not be relevant anymore.
2. Even if they are, they only prove that such practices are doable, or even desirable, but not that it's a necessary condition. Simple logic, i suppose.
3. On the other hand, so far I've played around 15 games as Axis, the longest being T11, and all ended with soviet player resigning. As mentioned among them only once was leningrade isolated. These are enough exceptions to the absolute statement. Also simple logic.
Well, at the end of day, in wars or wargames, arguments are proved not by talk but acts. So if you want to test my opinion by having a actual game, you are surely welcome. Won't take very long, I imagine