“Left-leaning” and “right-leaning” are somewhat objective. Add the word very to either, and suddenly we are much more in subjective eye-of-the-beholder territory. What’s “centrism” or “moderation” or “milquetoast” to one person will be seen as “radicalism”, even “extremism”, by another.
This is A. Not true, and B. Not the perjorative you think it is. The Guardian is as milquetoast and centrist as it's possible to get.