Funny enough, rowing, in all it's Olympic glory still isn't sure what the optimal oar size or length is. There's some contention over what the right surface area and geometry is with many higher performance groups using older designs now as they feel the current generation is oversized and with too short a shaft.
Olympic rower here - You're right there has been a shift towards Concept2 Comp blades in sculling (and with that a reconfiguration of oar, inboard, and outboard length). It seems sweeping is still firmly committed to big blades and I would say the oar length is fairly standardized in boat classes within ~1cm.
It will be interesting to see how many scullers (or sweepers) adopt the comp blades at the next World Championships and Olympics. I wouldn't consider those blades an "older" design, though feel free to correct me as I may not know my history here.
Of course, the "right" answer for racing may not be the same as for someone doing relatively recreational paddling. I assume it's very situational--including for the individual involved.
Recreational paddlers generally aren't going to notice a difference at all. The issue is balancing losses from force vectors, the blades pushing and pulling towards/away from each other at the extremes of the stroke, and fluid dynamics where the larger blade has higher flat plate drag and wastes less energy as turbulence around the periphery. You can't have both without making special (wider pin spread) rigging for the boat which oddly hasn't been played around with much.....
Also of note, lightweight women through open weight men use the same blade area and very similar spread/inboard/outboard measurements. There hasn't been much interest in tailoring the rigging to athletes due to equipment expense and availability limitations, even at the Olympic level.
In Olympic sabre fencing men and women use the same timings which can mean that the women's bouts are actually a fair bit more interesting to watch sometimes because they're slower and more likely to make mistakes whereas the men's game is a finely tuned collision at high speed in the middle of the piste (i.e. unless you fence regularly you'll have no idea what's going on)
