I don't disagree .. just that distances in "most" mobile setups have gear within a few feet of each other.
Mobile DJs were never a design consideration at that time. Unbalanced connections were used on amps intended for consumer applications. Turntables were the only consumer grade gear in a DJ booth of that time. While we think of the SL1200MKII as "pro gear" that's not what it was built for, and vinyl records were not a preferred broadcast source for professional music playback outside of a disco.
All professional amplifiers of that time featured either XLR inputs or block connectors for installation. The typical cable run to an amp rack in a club was 15 - 30ft and likely in close proximity to noise inducing rheostats.
It's not until late eighties or early nineties that you see pro-sumer class amps that feature combinations of RCA or 1/4" alongside XLR. Many were actually "pseudo-balanced" with varying results
In the clubs the mixers were either RANE or European brands like Meteor. It also might be interfaced with U-Matic video tape players which were broadcast quality XLR balanced. Then comes the Aux outs for lights, monitoring, delays, plus the mains to processing before hitting the amps.
Later, you could find Hi-Fi consumer video decks in a club (higher end) but the RCA audio outs were usually tapped to a Bogen line balancing transformer immediately off the deck to prevent noise and match impedance. Other than that - the only unbalanced links were to Technics SL1200 which of course were right in front of the DJ mixer.