I suspect if the chain derails were because a jolt caused the chain to jump or whip a bit (the rear der cage would play out a little then it's spring will pull tight again). If there was any back pedaling at the same time the chain's jumping could allow a derailment. This is very common when riding off road, hence the "clutched" rear cage pivot designs that have come to the market lately.

The squeak might be a hub seal rubbing against the hub shell. Some hubs have an outer "rubber" seal that sits on the axle and rides snug up against the shell. This interface can produce a noise often described as a squeak. A drop of light oil (Triflow in our shop) between the seal and shell cures this. A greater concern is if the seat post, handle bars or the cranks are the source. Sometimes an imperceptible amount of movement/wiggle can be happening and all that is observed is are creaks/clicks or ticks when really pedaling hard.

I also doubt that the spokes are going through so much stress that you can see then flexing. When you're moving around on the bike from the shocks and forces that jumps, drop offs and sharp jolts produce it's real hard to keep your eyes steady enough to discern what's actually happening. When the rim becomes permanently deformed (gets dented or flat spotted) you'll know that you've exceeded it's limits.

The FX series bikes are not meant to be ridden in the same aggressive manor as a mountain bike. They are intended for prepared and firm surfaces (pavement, bike paths, smooth dirt roads. As the cost level goes up (as in the 7.2 compared to the 7.4) the components get lighter, work nicer and potentially (with equal maintenance) have there better feel last longer. But some of the robustness of the wheels and tires is also taken out of the bike as a means to achieve the lighter and more responsive ride. Riders can ride skinny wheeled bikes off road without problems if they're skilled (cycle cross racing) and riders can bend strong mountain bike wheels riding on roads if they're not paying attention. How well your bike works and lasts is totally up to you, the rider. Your bike does not decide which bump it will ride over, or avoid. Andy.