This question about planning perk point allocation is pretty clearly off topic, however it is upvoted quite a bit (+20), has 46k+ views, and has quite a bit of good information. To delete it, it would take 5 delete votes to get rid of it, and delete votes can take a long time to come (there are a number of closed questions that are years old that still need a deletion vote). We have historically locked similar questions in the past, so the question is should we lock it or delete it? Either action will probably require a mod hammer.
The reason for the question off-topic is being opinion based. Per our guidelines, a question should be objective rather subjective to be on-topic. Even though is off-topic, it attracted many views, upvotes, and overall good information for future viewers.
From what I have seen, an off-topic question may be good in general terms, but they attract downvotes solely for the fact of being off-topic. This question only has a single negative downvote.
The fact the question is 6 years old, but only closed within the past 6 months shows how many users found the information useful, despite being off-topic. If the question is deleted, then the information will be lost without the proper privileges
My vote is have a moderator cast the historical lock on the question. The question matches 3 out the 4 criteria for a good historical lock candidate.
The post does not meet the current guidelines for a good, on-topic question, and
The post is stellar, in spite of its off-topic nature, and
There are a large number of views, upvotes and inbound links on the post
The fourth criteria states the question should be go through a cycle of close/open or delete/undelete at least once. However, a comment mentions users frequently desire questions to be locked without being reopened or undeleted. In this case, I am one of those users.