Whether you’re looking at a cheaper forged stem or something that’s been whittled, the same basic rules of leverage apply. The broader the clamp – either onto the fork steerer or the handlebars – the stiffer the connection will be for a given weight/wall thickness. You’ll also find some very fancy/funky designs from people like USE which actually work fine once you’ve fought the bits together in the right order. If there was ever a case for keeping things simple though we’ll take a fat, simply-forged stem with big 5mm bolts, over a brittle metal basket with tiny Ti bolts every time, whoever is endorsing it.
Interestingly while carbon stems are a thing in the road world, very few have dared creep onto the dirt and even then they’ve stayed firmly on the lightweight mountain bikes.