While this arrangement seems to be more common IME in the USA (e.g., Sushi Yasuda which employs several sushi chefs or Ginza Onodera NYC which usually has a chef at all 3 counters), it does happen in Japan. Typically in Japan (e.g., Hakkoku, and AFAIK Saito and Sugita), you will make a reservation with a specific chef (e.g., the reservation will be for taisho table or second chef table or third chef table, etc.), but there are still edomae spots in Tokyo with multiple chefs where they just seat you wherever (e.g., Ginza Onodera, Kanesaka - although you should certainly avoid the latter as it's hideously overrated).

There are, of course, many edomae spots in Japan that feature multiple assistants who prepare tsumami or even do some of the slicing/prep of certain sushi (esp. common with shellfish), as you noted.

FWIW, my experience at Masa was far worse (noting that it was about 10 years ago) and I've always strongly recommended people avoid Masa as a result (I've also refused to go to any establishment he's been involved with since). The service was terrible and as you also noted, the fish quality wasn't even that great. We were also hoodwinked by the reservations team into taking an early reservation slot, as they told us that being served by Masa was on a first-come first-serve basis - but when we got to the restaurant, we were the first party there and were told that Masa would be serving another party. The hostess didn't even apologize. And are they still charging the 20% "service" fee that isn't even for service?