I mean the one time I was in the US having breakfast or lunch at some random place. They had at least five staff milling around for twenty-five customers, probably more (staff I mean). You don't need to have two teens frantically going around with pitchers of water, just plop one down on the table and pay the remaining employees a good wage.
A good wage is not minimum wage either. Minimum wage is a "what is the least I can legally pay this employee", while as an employer your mindset should be "how much is this employee worth and how can I make them feel appreciated"
In the UK tipping is very hit or miss. Especially now that cash payments are becoming rare. I've noticed that food delivery drivers will be half way down the street by the time I open the door these days. They obviously don't expect anything. If there is a service charge on the bill I typically don't leave anything in particular, and I'd prefer it this way.
Often there's an 'optional' service charge on bills now (well, before) which we'll always begrudgingly pay. Only once have we asked them to remove it.