This does not make any sense. If you abandon the conceptual ideals of the Jedi then you are not Jedi any more.
That’s the point though. Once Luke abandons them, the Jedi no longer exist. He was the Last Jedi.
Edit: After rereading my original post, I think the confusion might be near the end where I said he “truly is the last Jedi”, where perhaps I should’ve said he “was” rather than “is”.
I see what you mean. But still it wouldn’t explain the reason for the title “The Last Jedi” if he hasn’t been Jedi for a while.