What is the origin of the phrase "to cut someone down to size"?

Solution 1:

The idiomatic expression does not appear to be as old as Middle Ages.

According to Etymonline it is the figurative usage of the literal one:

To cut (someone or something) down to size is from 1821 as "reduce to suitable dimensions;" the figurative sense, "reduce to the proper level of importance," is by 1927.

From The American Secretaries of State and Their Diplomacy, Volume 11 - Samuel Flagg Bemis. 1927

Wood wished to cut him down to size. Ainsworth knew it, and chose as a time for rebellion the moment when Wood and Stimson sought to abolish the bimonthly muster roll.....

According to GDoS it is of black AmE origin:

cut someone down (v.):

(orig. US black) to challenge, with the intention of proving one’s superiority, usu. in the context of verbal, dancing or musical competitions.

• 1946 [US] Mezzrow & Wolfe Really the Blues 231: All the contenders for the title [...] wanted to cut him down – that is, prove they were the best in the field.

• 1954 [US] Hepster’s Dict. 2: Cut you down – Put somebody in place.

• 1968 [US] G. Cuomo Among Thieves 216: It was to your benefit that someone like Penney tried to fag you early, as long as you could cut him down. The word got around, and people left you alone.

• 1994 [US] N. McCall Makes Me Wanna Holler (1995) 329: They cut her down without batting an eye.