Help with the endgame

I just reached the postgame in Monster Hunter Stories for the first time finishing any game in the Monster Hunter series.

I enjoyed it so much that Im determined to 100% the game and unlock all achievements.However, I feel way too weak for the endgame content. I read that I should tackle the Tower, but I can’t get past floor 17.

Right now I’m using a full Rathalos armor set and a Water Sword & Shield. My main Monsties are Ratha, Stygian Zinogre, and Pink Rathian. Even with Tier 7 gear, I still feel very underpowered.

For genes, I’ve been doing simple same-color bingos for raw power (I saw videos about hybrid builds but preferred to keep it straightforward). Still, I’m completely stuck.Any advice? I really loved this game and want to finish it before starting Monster Hunter Stories 2.