I love the ticket systems in places like Berlin, Helsinki, Heidelberg, and Tampere. They don’t use turnstiles at all, just occasional onboard ticket checkers.
It’s so much faster for large groups of people to move through the stations so it keeps people moving instead of piling up at a ticket machine, even ones as fast as those in London.
You don’t need officers standing guard at turnstiles, just extra onboard sweeps to keep most people honest.
Even better is a whole free system like some cities are going to. LA is having a freeway widening project happening. If the money for that went to their public transit system, they could make it fare free for 20 years at the same price point as “just one more lane, bro” of freeway that will still be a parking lot anyway.