Can't say I've had issues with people being mean... That's probably less down to it being Discord, and more just the community being shitty. Some people just don't like other people.
Being ignored is a pretty common thing though, I find. Again, it depends on the community, but it's more a problem with people in general than Discord, I think. Like, there are plenty of IRC servers that are just ghost towns. The main driver of that, I think, is the lack of purpose or cohesion in a community. Like, I'm in an ex-vtuber's Discord server, and the lack of actual community is blindingly obvious, because the chat's just completely dead until the v-tuber pops in every few months.