Personally, optimising a portfolio for diversification and fees is important - but never top priority.
Diversification just should be sufficient (and with fees, they somewhat counteract each other anyway).
Are you “maximally” diversified, when 5% of your portfolio is one stock / company (Apple)?
The Quality fund is the only equity fund I have in my finpension portfolio. We’ve had all the discussion about it and the reasons for that it here. The Quality index has consistently outperformed the “vanilla” World index over decades. Sure, that’s no guarantee for the future, but it’s the one “bet” I’m willing to take.
I think it has evidently held up for small caps. With emerging markets less so (though they’ve underperformed the developed world in USD for a quite a while).