Why Tone still carried a full forward gun battery

Was Tone's forward gun battery an attempt to evade the treaties or simply a use of the space left ahead of the aviation deck?

It mainly used the available bow space and preserved gun power for the decisive battle expected after the attritional phase.

The forward battery was not primarily a device for evading treaty restrictions. The aviation concentration left the bow as the natural place for the ship's guns. More importantly, Japanese doctrine expected a decisive fleet action after prolonged attrition, so every surviving gun still mattered at the end of the campaign. The arrangement joined the cruiser's scouting role to its continuing obligation to fight as a gun cruiser.