"I understand that if I drove round the arena unravelling duct tape as I went then it would create boring matches and be unfair"

Change duct tape to rope or cables and you have your answer. Boring matches and once entangled you wouldn't be able to disconnect from the other machine. Crushers have to disconnect after a period of time and demonstrate they aren't stuck on the other machine.

About the only way in the rule book you could get around it would be to use a tethered projectile and hope the tether gets tangled up. Again you would likely be disqualified if you couldn't disconnect from the other machine.

There's also the issue of safety. If the arena marshals have to enter the arena to untangle two machines they may not be able to access the removeable link easily if the machines are tangled up. I'm sure as hell not putting my hands near a robots weapon if I don't know the link is out so I wouldn't expect them to either.