*What? That's just daft.
There are exactly zero situations where knowing how to play tennis will save your life.
On the other hand, there are countless lakes, beaches, rivers, ponds, swimming pools etc that the average person will encounter over a lifetime.
Nobody is saying the child needs to take swimming as a sport. But a level of confidence in the water is far, far more important than being competent at skiing.*
Actually I don't think the comment was so daft.
As a non-swimmer I have encountered many lakes, beaches, rivers and ponds but I have not been tempted to put myself in a potential drowning situation by actually going in them. OTOH if I had what you call a level of confidence as a swimmer then I might enter the water and could therefore be at risk.
Just a POV.....
FWIW my DD had swimming lessons from 4 as I do think it is a useful skill to have and she can get enjoyment and good exercse from it. But as others have pointed out - a real life, scary drown-y situation prpbably involves strong currents and very cold water so average swimming skills might not be a life saver anyway.
Useful skill. Yes. Essential - not so sure. I am over 50 and have led a full and nomal life so I clearly haven't found it all that essential.