A Question On Building Topic Clusters

Hey everyone,

I'm a little confused on how building topic clusters work. I know there's a parent page covering the main keyword and then other pages covering the sub-topics. My question is: does this not cause keyword cannibalization?

For example, if the keyword is "designer watches" wouldn't your pillar page already rank for all the keywords related to "designer watches"? And in that case, wouldn't sub-topics like "best place to buy designer watches" cause keyword cannibalization with the pillar page?

if you create a separate page, titled "Designer Watches Shops", or "Places To Buy Designer Watches" it shouldn't cannibalize with the pillar page if you don't on-page SEO the pillar page for this keyword. At least in theory it shouldn't cannibalize because only God knows what google are up to these days...