The grammarians that you quote are on weak ground. There are other words that contain the notion of intensification. To give two examples, there are:

Cambridge
Intense
Extreme and forceful or (of a feeling) very strong:

Macmillan
Brilliant
Very intelligent
very skilful, impressive, or successful

The grammarian argument seems to be that a word deriving from intensification (very, extremely, gravely, even absolutely) of another word must not itself be intensified. This restricts the scale of intensification arbitrarily. It also expects users of a word to consider its antecedents, meaning and etymology before intensifying it.

As a matter of usage rather than semantics, this is clearly wrong, very wrong, very very wrong, extremely wrong, and absolutely wrong.

The grammarians that you quote are on weak ground. There are other words that contain the notion of intensification. To give two examples, there are:

Cambridge
Intense
Extreme and forceful or (of a feeling) very strong:

Macmillan
Brilliant
Very intelligent
very skilful, impressive, or successful

Both these words, and others, are often intensified by very.

The grammarian argument seems to be that a word deriving from intensification (very, extremely, gravely, even absolutely) of another word must not itself be intensified. This restricts the scale of intensification arbitrarily. It also expects users of a word to consider its antecedents, meaning and etymology before intensifying it.

Degrees of intensification are acceptable;
It is appalling (=very bad) that grammarians should adopt such an attitude and,
(furthermore)
it is very appalling that they presume to proscribe our usage.

As a matter of usage rather than semantics, they are clearly wrong, very wrong, very very wrong, extremely wrong, and absolutely wrong.