I don't think it's supposed to be a criticism.  I have never heard it used this way.

Is this a Scottish thing?

I think it's supposed to convey that a person is a dilettante/lacking in conviction.

Personally I think it suggests the person is flexible in the face of the maelstrom that is modern living.

I always saw it more as "don't worry, you win some, you lose some".  So I agree with you.

Other person is probably a twerp.

Stix: last time I heard someone say ‘win some lose some’ a european managing director in private equity lost his job, lolz.

just made me smile when I thought of it, he was a right twot too.

You could sing

Que Será, Será

But we'd all rather you didn't.

I don't disagree with than tbf

Save that only bits are cursed ground