Exactly. Well put.The whole muscle imbalance and structural asymmetry issue is quite fascinating from an entrepreneurial point of view. If you go to the chiropractor or physiotherapist and say your knee hurts, 99% of the time it will be due to a muscle imbalance or asymmetry. "You need to strengthen this muscle." I work as a strength coach and 99% of the time I'm trying to loosen up muscles to enhance performance and movement, not provide unwarranted isolated strengthening protocols. Frankly, I'm tired of physiotherapists providing strengthening and exercise programs. Just like Ange said, loosen up the region and provide general mobility, and 99% of the time when the athlete returns to sport, the strength required will also return. Tightness creates restriction and inhibition. Remove the restriction, eliminate the inhibition and guess what - people get stronger.
When Usain Bolt breaks the 200m world record, no one checks his leg lengths, finds a 1.5 cm discrepancy and then declares, "The slightly longer leg contributed to his fantastic performance!" But he pulls his groin and guess what! "It's his leg length discrepancy that's the problem!"
In the case of EMS, I would always try to train bilaterally even though one side may be less strong. In most cases, the weaker side will be upgraded (because it is well below its potential) and the healthy side won't be made disproportionately stronger (because it is likely closer to its potential ceiling). Remember, as Charlie often mentioned, EMS provides improvements in Raw Strength. It does not provide the coordination required for specific movements. Thus, there will be a transition period where coordination must be restored through specific movements (i.e. sprinting) to gradually integrate the strength improvements achieved through EMS. I believe only training one side with EMS may create a disparity that could create problems when reacquiring a skill.
(Of course the only problem with the above post is that it isn't as commercial as the other BS options promoted by the usual suspects)