I think you are being a bit harsh. It has a length wide colour breaking crease, so automatically we start at 4.0 and look if there are other defects. There's the obvious corner, so I would deduct another point. Now we are at 3.0. But beyond that, the other issues are all acceptable at those grades mentioned and don't make it worse. I am assuming the centrefold is well attached, as is the cover. So I would say 3.0.
That's a super cute book by the way, love that art!
Oh and to answer your question while there may be some evidence that there may be leniency towards age, it's really not a sure thing. For every example of leniency, I find an example of really tough grading. Same as any other era. So I would say that it's best to judge every era uniformally. Especially since grading is all about looking at the wear and tear. Check this book for example:
I think where people get mixed up is that flaws not brought upon by use of a comic (so like bindery defects, problems with colour, corner chipping, manufacturing tears and creases) are not judged as harshly and these manufacturing defects are more common in older books. But it's still the same rules.