He has always, always been this way since the juniors. Except as a junior his tantrums would be more self directed as there was no one else to abuse in that they were often self officiated. Also different is that he often reduced himself to tears on-court and off as a result. Yes. Tears.
He was a talent but repugnant since then. More reprehensible was that later in the professional ranks:
1) he had someone (or more) else to berate
2) the timing of his outbursts were never spontaneous anger, they seemed strategically timed to disrupt an opponent's concentration or run. His tirades rarely took place when ahead or if they did were not as long lived so as not to interrupt his own momentum on the way to a win.
Yeah, he did contribute to the popularity of the sport, particularly in the US where he and Connors represented the anti-heroes to Borg and later "a communist" Lendl.
But the type of "popularity" his behavior garnered, especially from the mainstream sports media, when they "went to the video tape" always appeared to be "watch this trainwreck" and relatively little notice of the outcome of the match or showing of Mc's tennis talent. It appealed to the masses in a sense, but the same masses who go to car races, though they are unlikely to admit it, not to see the shiny go fast cars but are actually waiting for the same kind of wreck.
His behavior as a teen one could almost be excuse as being an immature "brat".
As a full time tour pro? A calculated gamesman and/or cheat.
Now with "all the stakes" of a senior event in the balance it is still the latter and has all the sincerity of a "Pro Wrestling challenge" and has actually become a pitiful dark comedy.
He was and has always been an *****hole, albiet a talented one, which for some excuses all.