Of course they are linked, but removing the username from the comments means they are mostly anonymized as far as GDPR is concerned.
It is perfectly fine to unlink data and keep processing it, as long as its considered anonymized under GDPR.
Your post content here is also not considered personal data, it shows up on a lookup request because its currently linked. If i crawl the page and dont save the username, the resulting data can most likely be considered anonymized under GDPR as far as the current interpretation is concerned.
It only becomes a problem as soon as i become aware the content indeed did contain personal data or probably also if i could have expected it to with high probability.
And i'd have to make sure to remove obvious ways to re-link the content to your user (e.g. mentions of your username in comments).
Anything else requires precedence about ways to re-identify someone based on posts on a platform weighed against the users freedom and the difficulty of doing such re-identification.
Recital 26 discusses when something could be considered anonymous. (or rather when gdpr would apply at all, and what it means to have anonymous data)
mhh.. you might be correct.
I havent considered how easy it actually is to search for a comment and find the exact post.
Question is if searching indexers like public search-engines is enough to call the data easily re-identifiable.
Or if this usage of personal data is covered somehow else e.g. legitimate interest, weighed against the freedoms of the data subjects, as you have listed above already.