What difference does oxygen content of tea water make?
All moving water has dissolved oxygen in it. That is what fish breath

Dissolved oxygen is reactive, and will most likely extract more substances from the tea leaf, than without it. If these are the good flavour parts of tea, I do not know?

When you heat water it starts to release the dissolved oxygen. The more you heat water the more oxygen escapes

You can buy tea making kettles that bring water up to 95°C (203°F), but not boiling, so as to decrease the amount of dissolved oxygen lost, but still making the water hot enough to brew tea. They also save energy :-) I use one of these, and am happy with it

Example Kettle

Some people "watch" their kettle, and switch it off just before the water boils!

It is a personal taste preference if tea tastes better when brewed in water with more dissolved oxygen or not