I cannot wait until WoW is available so I do not need to use the battle.net client.

This is unlikely to be the case; Valve supports third-party launchers via Steam, so most likely this will not change the dependency on that

Overwatch on Steam does not require b.net, so I do not see why it wouldn’t be the case with their other titles.

I do agree with having to repurchase. I don’t really play D4, so I might just wait for a big sale if I do go with a repurchase.

Overwatch on Steam does not require b.net

Not sure where you get that information from, but the Steam Overwatch store page clearly says this:

Internet connection and Battle.net® Account required to play. A mobile phone number must be linked to your Battle.net® Account to play Overwatch® 2.

Not sure where you get that information from

Probably from playing it themself. Nowhere in the text you linked is stated that you need the client. Only a valid account and internet.

So no, Overwatch 2 on Steam doesn’t require a secondary launcher. Source: me, I play it on Steam.