If you are able to (and allowed), install an AdBlocker (e.g. uBlock Origin) to reduce the friction for such cases. In my experience these ads are rarely click-worthy.

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.