Not at all true.
You have a really weird mentality: you judge everything in the game from the perspective of a min-maxing power gamer, but one who is really terrible at the game. It seems your metric for what makes something good is whether it can reach a core population and factory count on par with the United States and Soviet Union.
Bulgaria is actually extremely powerful, even without expanding. It's more powerful than Hungary, but if you're using the Bulgarization of the Balkans focus you can core the same amount of things that communist and democratic Bulgaria can, so your point is wrong anyway on that count.
Not everyone plays the game to achieve a solo world conquest. It is fun just joining a faction and contributing to victory in the war. Bulgaria has more than enough industry to make some beefy armor or mechanized divisions that can easily beat out the Soviets.
Anarchist Spain is one of the worst choices too. Both Francoist and Falangist Spain are considerably more powerful. Again, showing that you see things solely in this silly metric of how much core population you can get.
Because manpower means more armies, more ability to fight and reserves for garrisons and such. By your logic that manpower means nothing, I guess Bhutan must be absolutely amazing to play.
Theres a reason why most content creators/big streamers like Tommykay and the like do Byzantium, Communist Bulgaria, Communist Mexico, Ottoman Empire, Austro-Hungarian Empire, Napoleon France, and the other more POWERFUL parts of a focus tree.
Anarchist spain allows it to core EVERYTHING as well as the massive buffs it gets to construction and such, means its VASTLY better than any other Spain. You get more factories and more manpower period. It's common sense that Anarchist Spain is superior to the others in terms of potential. Most players have more of my mentality than you realize. You understand that your historical, allies win 2.0 mentality is part of the minority right? You're vocal for sure, but you're in the minority. Most people don't want to just join a faction and be carried. They want to -do- things. Its WHY communist Bulgaria is played more because it's BETTER than the Non-aligned part. The ability to swap other countries to communism, invite them to a faction/puppet them and then core them for FREE is phenomonal. Non-aligned can't do that. It requires you to conquer to core and good luck with that.
It's not a silly metric, manpower + Factories=A stronger nation=More potiential=More things to do in a match=better.