Water and gearing

Very definitely need to address the gearing as those are like a 32 inch, which is huge on standard gears.

Don't forget the water going under the car also has more room now we know that the car is so much taller than standard.

Sports cars are low to increase down force by reducing the air pressure under the vehicle and then have flat floors to induce the venturi effect further reducing the air pressure. The hydrodynamic forces acting on a semi submerged jimny cannot be assumed to effect it in the same manner as a solid block of similar dimensions making contact with the bed of the watercourse. Yes an account can be taken for the turbulence offered by the components under the vehicle but they will still allow a significant flow compared with the previously mentioned solid block.

Yes an no. Torque is the amount of work that can be done, power is that work being done over time. So by lowering the gearing either by selecting a lower gear which is not possible if you're already in the lowest one in the gearboxes or by proactively installing an entirely different set of lower gears you are able to have the engine work effectively in a rpm range where the available power is higher. There is no contradiction.

As to using a more suitable vehicle for wading I would suggest that partially submerging any vehicle regularly that is not specifically amphibious is going to cause maintenance issues at which point if you are going to be regularly fixing it anyway it doesn't matter what vehicle it is. Though personally if it were that regularly I might consider a boat or hovercraft.