Portinfer and me hail from the same location. He's already mentioned the importance of local conditions. Lots of other replies do the same. However lots of other factors come into it.
I've been freediving for 40 years. Most of that time I've never needed to dive deeper than 10 metres and probably couldn't have. Most of my fishing was done in less than 20 foot (6M) and quite a lot in less than 1 metre. Despite this I have been a local champion, caught thousands of fish and held endless records.
Only recently with new blood (like Portinfer) and new equipment and new techniques have people started to go deeper, at least locally. Sometimes going deeper works and sometimes it doesn't.
Dave
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