Steve Jobs and Tim Cook have both stated that they don't hesitate to cannibalize their own products, and Apple has proved that many times over.
Especially at the scale in which iPad having developer tools could ostensibly cannibalize Mac sales — there's no way this would be a factor in the existence of those tools.
We saw a huge push to bring the mac near iOS territory (the Mac Store, gatekeeper, catalyst, the new design language etc.) . If Apple could, I bet they'd exchange every new mac for an iPad and effectively gain the tightest control they could ever get of a huge part of the ecosystem.