This is really an excellent question that must be looked at by every player.
It is good advice to play people better than you, which forces you to pull out the best stuff you've got from your arsenal. .. no doubt.
At the same time, a tennis player has to develop confidence. This comes from playing and winning. My advice to you is to find a tennis sparring partner to play who is not quite as good as you, to play every so often, to beat and upon whom to try new strokes and strategies.
Back in my heyday, I would play most of my competitive stuff on weekends, but during the week I would have one or two tennis friends, not quite as good as me, to play on a more relaxed basis. This lets you feel good when you beat them; it lets you try out different things that you wouldn't dare risk in a "real" match.
You sound like you need a patsy.
To Praise, To Bless, To Preach--the Dominican Order