I don't think these are very relevant for the average aikido practitioner during practice. The implied health benefits, however... OTOH, one could also argue that similar health benefits are easier to gain in the gym.
Stability isn't important during practice? I think that most Aikido people really underestimate how unstable they are, and how much stress it puts on their body.
The "better in the gym" argument is, for me, a pointless argument. It would be better for my flexibility to do ballet - but I don't do ballet.