宅配便 for tourist groups?

Hi there!

I am an organizer of a sister city junior high school group trip that just returned home from Japan on June 16th. The (non-Japanese speaking) adult chaperones reported that shipping luggage with kuroneko-Yamato seemed to have gotten a lot less friendly in Tokyo and Osaka and slow and it seemed like Sagawa wasn’t really a viable option because of inconsistency in things like pricing and speed. I don’t think they knew of other carriers to try.
Despite phone calls from our Sister City’s international office trying to help, in one case this 12 member group had no option but to take their luggage on the Shinkansen. They were trying to do the right thing but were forced by circumstance into this action that I have been told would cause train staff to have a (figurative) heart attack. The effect all of that luggage must have had on others in that train car is concerning to me.
I understand that over tourism has become an issue and I am looking for some perspective on the situation. I have heard of barriers like this appearing in Japan before but have not personally experienced it. I am not confident that the language barrier wasn’t the real problem. Can anyone shed some light on this and if possible suggest how this group could do better next year?