Or "Naruto is the original series and this is just my fun spinoff."
It is not his fun spin off though? He's hired to interpret and write. It is certified canonical part of Naruto main/manga timeline by Shonen Jump, the owners of Naruto.
Jun is hired to write it under their banner and Kodachi, sole writer of Boruto's up until 2020, supervision.
If Shonen Jump decides something is canon, present them as canon, ask Kishimoto to illustrate for them under that banner, ask Kodachi- the main author of Boruto who comes up with story flow and plot of Naruto going forward all on his own- to supervise them, and them release them under official timeline, then they're canon.
Again, call them not Kishi's work and you're right. Call them non-canon and you're wrong.
Boruto gets special precedent due to Kishi working on it himself on and off and his approval for it, same with The Last.
Kishimoto himself claimed he is separate from Boruto for most parts, is often on trip and vacation after the ending, and just checks over stuff once made.
Boruto was never Kishi's story to write other than tweaking inconsistencies until 2020.
Kodachi was sole writer, and one who came up with and delivered the content as well as story-writing. Same Kodachi who supervised novels.
All plots, entire story, everything were from Kodachi. Same one who supervised the novels.
Kishi had to sign off and give his approvals to that as well.
Kishimoto signed off, illustrated and gave approval to Light Novels as canonical material, because that's what Jump presents them as. Anime filler is not. Movies are not outside of The Last/Boruto.
Hell, they're literally follow-up stories stated in Last Chapter of Naruto. Are part of official time-line by Jump, and are literally supervised by author of Boruto.