mastodon cw's are like "TOPIC [show more]", on a line by itself, in a style that mostly matches the style of things around it. one click and you're in. it's a speedbump.
cohost's are like "This post has content warnings for: TOPIC [show post]" with a colored border, much more visually set off. again, one click and you're in. but it looks like much more of a roadblock.
speaking as someone who likes mastodon's cw system, i feel like people are misunderstanding it. it's for introducing a topic, to let someone interact with it or not. you can set them to automatically have the post open if you want. you still see the cw, but there's nothing in the way of your reading flow, if that's important to you.
cohost's are they're more specifically focused on the warning part, and i think this has a lightly elevating effect. people say things like "whoa, people on masto have to cw food", like yeah of course we do (though we don't have to), it's a tiny ask.
i don't want this to be read as "cohost bad" or "the cw system should change", i like both of these networks genuinely a lot. it's two different vibes. just like, i get why cw's might rub people the wrong way but they can be done usefully. and complaining about em is big freeze peach energy.
edit: realizing that last sentence could come off real insensitive. there are some valid concerns about cw's and reasons to not, in certain cases. i haven't been very nuanced here, i thought i was just going to talk about the UX of the thing. i'm overreaching but i'll leave it for now.