Focus keywords: aim for lower-competition long-tail, or go for the bigger/broader term anyway?

Getting mixed advice and want to sanity-check it.

Some people say: pick a narrower, lower-competition long-tail phrase for your focus keyword - easier to actually rank for, faster wins, especially for smaller/newer sites.

Others say: go for the bigger, broader (higher-volume, higher-competition) term even if it's harder, because that's where the actual traffic is and long-tail alone won't move the needle.

For context, I'm doing this for individual e-commerce product pages (not blog content) - each page targets one specific product variant, so the "obvious" keyword is usually already fairly narrow/long-tail by nature (product name + material + size, that kind of thing).

Curious how people actually decide between the two in practice - is it purely site authority/age based (new site = go narrow, established site = go broad), or is there more nuance to it? And does the calculus change for individual product pages vs. blog/category content?