That certainly lines up with my experience at Tokyo where I stayed twice last September:

• The first stay was Sunday-Thursday when it was pretty quiet. As others have mentioned the hard product is incredible, and having the pool to ourselves was very nice. Service was OK, in particular with the concierge and friendly door staff, but breakfast was consistently error-prone (forgetting items, asking for 1 of something each and getting 1 to share, etc) but nothing that got us bothered.
• Contrast this with a Friday night stay the following week when it was incredibly busy, the lobby was packed, and staff seemed very flustered. At breakfast my wife received her order and I gave up waiting after 30 minutes and just left - no service recovery though I didn't bother complaining since it was our last day.
• I'd still return for the hard product, and would just have low expectations for service if there during a busy period (apparently that's always now?).

At Venice service was much better and more polished, though as others here have mentioned one has to find a phone and call for anything when in one of the many beautiful lounge spaces, whereas in the non-city locations it wouldn't be as hard to find a staff member.