I'd argue it's just the opposite.
See, if the Alphabet Man knew I frequented both Discord and bus-stop.net
and they wanted to track me down and they had compromised both services, which of them do you think they would start looking from? Having to search millions of Discord users and their message logs would be a needless burden compared to looking at some 20 active bus-stop.net
users and figuring out which one of them is me.
Regarding advertisements, how do you know this message isn't an ad for soap? You wouldn't expect it and couldn't tell because it's anonymous. Unlike on Discord, where you could check anyone's message history to determine whether they're an ad bot or a legitimate user.