Well, japan has the H6k4 which at tier 1, is a beast for loving up a fighters day. Also it can unlock 2 800lb bombs that insta-kill enemy bases so...
Yeah, also the speed. The loving speed of that bomber... Nothing, not even a PBY-Catalina can stand up to this thing. Its not even worth the spot of tier 1 its more like tier 2. Also japan is extremely good. I don't see why people hate/complain that Gaijin isn't giving them a boost. I've out maneuvered spits and LaGGs. Now that's something.
Then you're not fighting competent opponents. Japan lost it's air superiority in the pacific for multiple reason, but the largest one being US pilots getting smart. As soon as your enemy realises, "Oh I should just NOT turn and fly away." You're done for. None of the A6M's can keep up with anything at their tier (let alone fight any of their historical counterparts) and a good boom'n'zoom pilot can fly circles around a single Japanese pilot. A6M's are the most fragile, overtiered, overpriced aircraft in the game and it gets worse with every update. Luckily the War Thunder playerbase is horrible in arcade and the A6M's turning will outfly anyone in arcade furrballs.
That being said, I fly Japan almost exclusively and the Japanese bombers are nothing to laugh at. Most of the bombers are small, fast, and agile with horrible bomb loads and excellent defenses. The H6K has the best defense and bomb load for it's tier and I cannot wait for the H8K.