I will talk a lot about this in my level 60 post so I will make it simple here.
How do people(non-natives) become good at English? With a ridiculous amount of input. They don’t become good because they started talking with their friends in English. I mean, yes, that might happen when they play video games with a friend but the amount of input they get overall is tremendously high compared to the output.
I mean what do you want to say early on anyway? 私はペンです? It’s useless. Unless you want to be like one of those people on YouTube(I learned a language in 7 days), talking very early on isn’t gonna bring much to the table. The reason why people like the idea of starting to speak early is because it’s motivating. However, that doesn’t mean it’s efficient.
This brings me to the second part which is that your accent will heavily suffer. I am not here to debate whether AJATT is good or not but they are right when they say you need a lot of input first if you want to sound close to a native speaker. If you aren’t used to the different sounds first you will ruin yourself.
Imagine someone who never watched any Japanese show trying to learn the language. He uses some textbooks and starts speaking as he is learning. The problem is he doesn’t have the right sounds in his head yet. So what he is gonna do? Imitate/create the Japanese sounds using the sounds of his own language. This will result in having a very weird accent. Not only that but his pitch accent will be completely destroyed.
Yes, he will be able to speak. He might even impress some Japanese learners but he will sound funny to natives. I mean, it would be sad to ruin 3 years of Japanese studies because your accent is awful. It’s insanely hard to fix a bad accent.
So which one do you prefer? The short term win or the long term win?