Go Ahead and Replace All

I have a 2019 Honda Odyssey. At somewhere around 30,000 miles, my owner’s manual says I will need to change the transmission fluid. The Honda dealership says that they only change a portion of the fluid, for whatever reasonThat makes no sense to me. A partial change is like doing a half oil change on your engine. I asked about the shops that have a machine that hooks into the transmission line and pumps all the old fluid out and new fluid in. The dealership said that was not a good idea because junk in the transmission could clog the lines.That much junk, after 30,000 miles? I will probably go to a shop that uses the “full change”