Considering HOI4 is probably the most successful Paradox game ever, with the largest active player base (and one that is constantly growing), I think it's hard to criticise the current direction of HOI4 for not being profitable enough or for not attracting a large enough audience.
Sure, there's stuff I don't like (the AI and bugs, mostly), and I don't want Paradox to move away from historical content, but the current balance of historical and alternate history seems to work well for them. No one can prove that Paradox wouldn't make millions more if they made more historical content (or focused on improving core mechanics over adding alternate history content), but we can see with some certainty that the current direction is working. As long as the game is growing and selling, there's very little incentive for Paradox to go in a different direction with HOI4.
We can compare HOI4's popularity with more historical games to get an idea of what customers Paradox is missing out on. The OP used Strategic Command WWII: World at War as an example of a more historical game, but that game has an concurrent player base of about 90 people. Unity of Command was also mentioned, and that is in a similar position when it comes to active numbers. There's the various Gary Grigsby titles, but they're even smaller. Obviously these aren't perfect examples: These are much smaller games made by smaller companies with a smaller following, they don't have the same resources or the ability to market their games to hundreds of thousands of interested buyers (see: the new launcher), but if that's the biggest competition on the historical side of things I don't think Paradox has anything to worry about.
Where is this hypothetical large audience of history-lovers who like grand strategy WW2 games but refuse to buy HOI4 due to its alternate history content?