Sorry to see arduino still has this issue, which could very like happen to me.. I have long projects. OP, I bet you can reduce your footprint by doing concise texts. Why should these messages be so long anyway? An alternative is to store them on an SD card. You probably have enough pins for that. Third option is to find duplicate messages and use pgm_read_byte. The flash helper never optimizes for duplicate messages.
Anyway good luck to your project. Anyone reaching such limit genuinely should be applauded for their work.