I think your definition of "reach" may be too narrow. There is horizontal reach (reaching more people) but also vertical reach (reaching different people).
To me, Bluesky is better at both. Mastodon feels very much like a closed ecosystem where I'm mostly exposed to the same type of people every day unless I go out of my way.
On Bluesky, almost every day I'm running into someone unexpected discussing something unexpected. There's more serendipity.