Indeed, the whole point of ignoring somebody is usually because they are annoying to you and/or draw you into an argument. So it really seems to defeat the purpose when they are displayed in /latest etc.
Fortunately this is available and seems to work well:
https://github.com/notedboi/discourse-ignore-plus
But it really feels like it should be a core Discourse feature, at least as an option, or ideally by default.