Sure, could be their environment simply didn't change. In which case, a simpler, less adaptable organism may be fitter than a more adaptable one (if the cost of adaptability was higher).

Species go extinct all the time, there are always very unadaptable species around and most of them go extinct pretty soon after they become unadaptable because environments change all the time in the grander scale of things.

Right, fitness can only be understood in the context an organism is in at the time. There is no long term plan.

An adaptable organism might stay around for longer - or it might be outcompeted in the short term by less adaptable organisms.

Over time, being adaptable is what really matters for survival. If something could adapt perfectly, it’d always come out on top.

Sure, “survival of the fittest” in the short term is obvious, but it’s hardly worth pointing out.