When used grammatically as intensifiers, these words cease to be degree adverbs, because they no longer quantify the idea they modify; instead, they emphasize it emotionally.
[1] Intensifier is a category with grammatical properties, but insufficiently defined unless its functional significance is also described (what Huddleston calls a notional definition[2]).
A speaker or writer's use of the characterization encourages a reader or listener to consider and begin to feel the underlying emotion.
[8][9] That finding agrees with the presumption that CEOs attempting to hide poor performance exert themselves more forcefully to persuade their listeners.
David F. Larcker and Zakolyukinaz give a list of 115 extreme positive emotions words, including intensifiers: awful, deucedly, emphatically, excellently, fabulously, fantastically, genuinely, gloriously, immensely, incredibly, insanely, keenly, madly, magnificently, marvelously, splendidly, supremely, terrifically, truly, unquestionably, wonderfully, very [good].
A 2013 Forbes Magazine article[10] about counterproductive modes of expression in English specifically discouraged use of really and observed that it provokes doubt and degrades the speaker's credibility: "'Really' – Finder calls this a 'poor attempt to instill candor and truthfulness' that makes clients and coworkers question whether you're really telling the truth."