I'm a former english teacher from the tiny country of Belize, ive spent most of my life between japan and korea, im also a hobbyist polyglot.
I speak Garifuna, English, French, Spanish, Korean, and Japanese. I've been teaching myself languages since I was around 5 years old. Im very lucky to hold n1 certification for Spanish and Korean. In 3 years I'll be adding Japanese to that.
For starters, 3 years is an extremely short amount of time to dedicate to a language.
Language learning is a lifetime endeavor, not a destination.
Secondly, if you want to learn a language as an adult, unless you somehow scam someone into teaching you for free; you are going to have to hire a tutor.
You have to essentially build a life around learning languages if you want to learn them.
I've met geniuses who pick up language basics as effortlessly as a cat laps up cream from a dish, who cant learn languages because they dont have the mindset to be able to stick to language learning for their entire lives.
I'm saying all this to say, actual language learning is extremely easy, the hard part is being consistent and sticking to realistic goals.
I've met so many people who want to speak Japanese, but aren't willing to study for even an hour, let alone the 3-4 hours a day you need to study if you come from a non-asian background.
Japanese might be hard for you purely because of your mindset
Although I understand your point of view, that does not work for everyone, as you say. I regularly meet japanese people, and some are teachers. I also meet tons of japanese students and the explanation is always the same: students who are good at learning are always telling japanese isn't difficult. Teachers who are teaching are always telling japanese isn't difficult.
People tend to compare ones to others, and "if you've got brain, you can learn it". Sure, we can learn everything, but every brain does not work the same way.
Learning is a procedure of persistency, the more time you invest, the more you advance. That's logical, but in the process of learning there are other factors involved.
Tutors can help, but they are not mandatory. I know we won't agree because you're one of them, but rest assured that in my life I've seen it many times. Because learning languages is one of the cheapest things (money related) and most expensive things (time related).
Brain is limited, and whoever tells me the opposite mean does not understand how mine is working. I am very bad at learning languages, but I've learnt spanish, catalan, english, a little bit of portuguese and a little bit of japanese. That would be fantastic, isn't it? actually no, it's not. I tend to forget words in all of them, I constantly find myself stuck in a conversation in my mother language because I can't recall words that are simple to other people. Why? because brain can hold a limited number of words and knowledge, depending on how smart it is.
If you want to tell me I am not good at japanese because I don't study 4 hours a day I can understand it, but as it happened before, even if I did you would be surprised how bad someone can be after studying and investing 4 hours every day after 3 years. Probably you would think I am not studying 4 hours a day when I am totally doing it.
The process of forgetting is also brain dependant, and that can't be helped, you can train your brain to some extent, but it has your own pysiological limitations.
Everyone can learn anything, some people need much more time than other, so we need to balance if the time we personally need for something is worth investing in exchange of the gain we are receiving.
