This is factually incorrect and I wish people with little or no exposure to modern strength and conditioning would stop talking about it until they earn an opinion the way everyone else has to: with a couple years on some rings or under a barbell.
Olympic weightlifting, powerlifting, bodyweight conditioning, gymnastics, swimming, cycling, rowing, and jumping rope are all multi-articulate movements that use as much of the body as possible, as intelligently as possible to accomplish tasks.
The much ridiculed discipline of bodybuilding is the *only* area of "western" training that isolates specific muscle groups, and you have trotted it out as a straw man with which to knock down a huge range of disciplines backed by success records going back in some cases thousands of years.
To my knowledge no one has ever suggested bodybuilding as a path to developing martial arts skills, much less as an alternative to internal skills. Few athletes other than bodybuilders even considers it a fitness methodology because of a long track record of poor skill transfer to other activities, a drawback that is widely assumed by everyone else in fitness to be the curse of training muscles in isolation.
Note I am not implying that any of those disciplines will serve you better than internal training in developing Aikido skills, I am merely trying to clear up the factual errors being presented.
I stand by what I said regarding the "prevailing western take" regarding isometrics and dynamic resistance training. Remember: the prevailing beliefs are those of the public at large. When the average Joe or Jane signs up for a gym membership with the thought of doing resistance training, what is he/she typically shown and sold (see photo below)? How many people who have greatly benefited from resistance training for years maintain a disciplined schedule of "upper-body days and lower-body days", whether they do high weight, low reps, or vice versa? Etc.
Also, based on my experience, I agree with you regarding isometrics. I didn't equate it to bodybuilding, but rather specifically pointed out a regimen for rehab was imparted to me: very different goals. And, also to your points, the reason the coach suggested isometrics was to strengthen more than just a given muscle, but rather everything needed to stabllize the knees. Nonetheless, the focus was specifically on muscles, which IP/IS training expressly avoids.