Why shouldn't Germany be able to build "150 CIC before Danzig?"
Germany had 2.5 million in the Wehrmacht at the time of Fall Weiss. Arguably, the fraction of the population which supported any party other than the Nazis was ~0% Certainly it was IMPOSSIBLE to express opposition to the Nazi party, so why should it even be necessary to have PP costing aspects like "ban democracy/communism" or "party raids?" If the game seeks to be informed by history, it should NOT be necessary.
Germany had something like 86 infantry divisions, 8 armored, and 12 motorized, and in the ballpark of 2000 aircraft by the time of Fall Weiss. They also had a couple score Type II and a few Type VIIC submarines, which were actually reasonably effective right from the beginning.
I would say that various indirect lines of evidence suggest that the stability and popularity of the German regime INCREASED substantially by December 1939 after the defeat of Poland, and then again a year later once the Denmark, Norway, Netherlands, Belgium and Luxemberg and France were wrapped up, and England had been kicked off the continent. Yugoslavia was a cakewalk
Despite Hitler being an utter idiot when it came to grand military strategy, and many in his inner circle being one manner of incompetent (if not several manners all packaged into one) and despite the Wehrmacht not being substantially larger than the French army (nor necessarily any more "advanced") the Nazis steamrollered Poland, France, the Low Countries, Norway and Denmark for a grand total of no more than ~195,000 total casualties (Battle of France ~138k killed and wounded; Operation Weserübung ~6000 total; Fall Weiss ~50,000).
In all of my play on Regular difficulty as Germany (the only position I have played since buying the game a couple weeks ago), I have made it to ~1941 at least 7 times and then restarted for various reasons. I have been playing strategy games since 1984, so while some problems I have suffered in initial play might be attributable to unfamiliarity with the game design, I think I qualify as an "experienced gamer."
In all my experience, I have found that achieving what the Nazi regime achieved by end of 1941 is, perhaps not "impossible" but involves a high degree of careful analysis, exacting attention, and excessive micro-managing. Out of the 7 or 8 attempts I have "succeeded" in achieving what the Nazis achieved a grand total of zero times. First of all, my casualties are always enormously inflated, up into the multi-hundreds of thousands. THAT excludes me from claiming "success" at achieving historicity.
Poland generally takes about twice as long, and this I attribute to the way the capitulation mechanic was changed, as well as perhaps the fact that I never use Molotov-Ribbentrop.
France holds out for far too long in my experience, though again that is perhaps a result of me seeking full annexation and not allying with Italy (because in one session Italy annexed all of France!).
I have yet to even bother with Weserübung simply because I have focused on trying to achieved the larger objectives in a relatively historical manner before adding the somewhat more optional objective to the mix.
With all that said, from my standpoint, as a strictly singleplayer mode user, I would say that as of 1.51 "something was not right" in how much resistance a German player met in attempting to repeat historical outcomes. This doesn't necessarily mean that Germany needed buffing; in fact I suspect that the problems have more to do with certain game mechanics than with Germany specifically, but it also doesn't mean that Germany needed debuffing.
The views of multiplayer mode users MUST be kept strictly separate from those of singleplaye mode users, and this is why I am so adamant and outspoken in criticizing this manner of packaging and selling and supporting the product. It is a colossal blunder to try to make one rule system work for both modes of play and none of us should have to suffer through it.
The ball is in Paradox court: fix the game by doing a branch in the .exe so that there are effectively TWO games in one and discussions about the two modes are always kept separate. Make rules changes suited to balance MP as needed and without consequence for SP mode; likewise make changes suited to balance for SP as needed and without consequence for MP mode.
No game company is going to create what would be effectively 2 games for separate audiences. It would require them to almost double their assigned content, coding, and QA staff on the game. Especially when MP play is at best 15% of their market for HOI4.
This is why there are mods specifically for MP play.