Currently Japan has no attacker planes beyond BR3, causing not only disparity between factions but also making Japan effectively only have one hotly contested plane slot for high BR. Making the Kikka an attacker would fix this issue, and be more accurate, as it was historically designed as an anti-ship attack aircraft. This resulted in the low ammunition count and high payload, making it far more well suited for the attacker role ingame as well. This would also remove the need to find and add a new attacker plane for high BR japan, something important, as from what I’ve seen of others researching it, few good options exist.
While this plane is considered a fighter in War Thunder, which I assume the fighter role was carried over from, the official wiki describes it as an anti-ship attack plane, and I assume this choice was made just for airspawn balance, and it should not necessarily be carried over into enlisted.
To add to this, I don’t think this will seriously increase HE spam either. A kikka will always be up in br5 regardless, doing this would just add a fighter alongside it which will have a very mild payload compared to anything the US has.
tl;dr change the kikka to be an attack aircraft as it was designed to be irl, this make japan not be effectively limited to just one airplane in high br