I can see where you're both coming from on this...
What I have noticed from my fairly lengthy experience of triples is that a shorter crank than you might be used to has a better feel in the granny ring of a triple setup.
Similarly, standard doubles benefit from the extra leverage of a longer crank... Although I have relatively little personal experience of this in recent years.
I have triples in 170, 172.5 and 175 and whilst I can feel more at ease spinning the granny with a 170 I can use a higher gear on the same hill with the 175.
As a lifelong masher I am, overall, slightly happier in in 175 or 172.5 than 170 but over mixed terrain I've found it makes bugger all difference what crank length I've gone out on.
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These are all just one ring though so you still need to factor in the cost of a granny ring and possibly bolts too.
The longer bottom bracket would also still be required with any of these options.
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