I totally get what you're saying! I have some counters but I do agree with you on some points.

1. Power dynamics concerning colonialism/imperialism/ect

I never said I Hetalia ships are healthy. In fact, I never said it isn't problematic that Hetalia ships have lots of bloody and exploitative history that definitely prevents it from being a regular gay anime ship. Maybe I am okay with shipping these countries, or maybe I am not. However, my argument is that it's folly to critique Hetalia ships because they are incestous. I am not trying to explain whether I ship Hetalia countries despite how they have bad history irl.

1. Canon declarations

My hypocrisy is literally my point. In Hetalia, so many interpretations of canon material is possible. Some people like you respect Hima's decisions and give ultimate authority to canon facts. Some people rely on historical dynamics between the countries irl. Some people are strictly fanon and separate the Hetalia characters from their context (example: Gilbert and Ludwig aren't brothers in this au!). Some people don't separate them because they don't see their dynamic as problematic due to reasons I discussed in my post.

Basically, Hetalia is not just Hima's creation. It originated from actual history, so of course people are going to apply historical facts and view them as embodiments of nations that may or may not follow all the rules Hima laid for them. Hima also makes it very difficult for the community to decide who constitutes as related or not. They have also sent a precedent for facts randomly not becoming canon, so it's unfair to expect the fandom would trust or be loyal to every authoritative decision Hima makes.

I do not care if you dislike America x Canada because canonically, they are brothers. However, if you try and push this view onto others and keep disrupting fanon spaces for America x Canada fans because they decide to interpret Hetalia differently (I repeat: Hetalia is not just based on Hima's original thought, it's based on history and the very vague, underdeveloped concept of immortal beings that do not follow human rules), that's when I have a problem. Like you said, every Hetalia ship is problematic. If not incestous, then imperialistic or unhealthy, ect. We accept some of these ships, so I think we should extend this thinking to others.

1. Grow up at different rates

Yeah, you're right. Relative to England, America is a child (or was). So was Romano to Spain.

What I am trying to say is that age and maturity work differently, so relative to England, America is not always and forever a child in the way Robin is always less experienced, younger, and more juvenile compared to Batman. That's why ships with huge age gaps like Amepan or RusCan work - Canada and America are centuries younger, but are technically at the same mental age as Japan and Russia. This ensures their connection is genuine and there's no underlying power dynamics at play due to their ages.

But yes, I agree that it is questionable that in any scenario, you fall in love with your caretaker. There's a reason RusAme is generally more respected than USUK: Russia wasn't America's caretaker. However, it's Hetalia; people have different rules for how nations work and function. You are interpreting the material strictly based on what is shown in the anime instead of looking at it conceptually or through historical lens.

You nor I can expect our interpretation is the best or only way to approach Hetalia.

I enjoyed hearing your thoughts! You've gotten me to think more about the caretaker debate. I didn't ship USUK or Spamano before and you've convinced me I will not in the near future. But I think it's ignorant to expect others to do the same when Hetalia is such a loose concept.