Oh gosh..... I am about to say several things and I hope none of them sound incredibly stoopid, but some of it might.
First, there shouldn't be a job that depends on voluntary tips from other people. Somehow this system may have made sense (or not) whenever someone first thought it up, but it seems amazingly insufficient now. Not that I know the answer for a solution short of you would get paid a fair hourly wage just like any other job.
Sometimes it may be a matter of misconception. In a day long ago, a tip was more understood as "an extra for good service" meaning that if you didn't think you got good service, leaving a small tip or none conveyed that sentiment and was incentive for the wait person to make good effort. As for today, it still matters to me about the level of service I am given. If someone doesn't give me decent service, I am not as inclined to want to pay the same tip as I would if I got good service. Yes.... I believe it is human nature in that regard. I am not someone that looks for a reason not to give a fair tip..... but it still matters.
I do know good service is given sometimes that is not rewarded properly and that is unkind. Unfortunately, the world doesn't seem to be getting kinder or less selfish. Most restaurants I am aware of, would add an automatic gratuity if the party were as large as your friend's, to make sure something like that does not happen.
Although I'm not sure how, today it is possible that some people don't understand that the tips are the majority of what the wait person makes. Unless someone knows someone in the industry or has just accidentally read about it, they may really not know. Although it has been many years now, I remember being astounded at what a low hourly wage a waiter or waitress was paid not counting tips. That never sounded right from day one to me and it still doesn't.
I have a friend in the industry who fortunately is blond, thin and bubbly, so in general, she makes a pretty good haul on tips in a chain steak house restaurant. That is the only reason I have been aware of this predicament.
One more thing..... a wait person's tips needing to cover a bartender, hostess and busboy blows my mind. There is a lot that does not seem right about that to me. I'm sure there is an inside view I don't know a bout, but that is entirely too many people's fingers in one person's tips. I hope one day there is a better way.