The Philips LDK5 ( descended from the Norelco PC100 ) had the overwhelming advantage of Triax camera cable. For outside broadcast use the change from TV36 cable to Triax was amazing.
I don't think that the use of 25mm tubes made the LDK5 soft, tube technology had moved on by then. Any plumbicon camera looks soft with the AP turned off.
Regards Brian,
www.tvcameramuseum.org