I've done some research into giant arthropods lately. The largest land arthropod currently is the Coconut Crab, but I'm wondering how much bigger an arthropod can get in our current Earth climate and environment (atmosphere, gravity and range of biomes specifically) before needing some drastic evolutionary design changes. For example, how big could the biological design for a spider or an ant be nowadays? I've heard of the insane sizes Myriapods have been in the past, can other arthropods do that too, let alone on our modern-day earth?
I'm aware there is, has, and was larger species of arthropod, but these were either underwater, alive during a time where there was more oxygen in the atmosphere, or both. What could be done on our modern range of land environments here on Earth? Can we get arthropods any larger than a coconut crab in today's climate?