4E invented "shouting at people to just change the flavour of stuff if it's not in the game yet". When the game dropped, people had some real questions that needed answering:
- Where are the Monks?
- And if I wanted to play a Druid...?
- How the fuck am I supposed to play a Necromancer?
- I liked Bards. And Gnomes. Would you be so kind as to explain this shit?
- Where the fucking fuck is...
Given the game, designers and fanbase were going out of its way to tell you to "stop fucking around with shitty old editions you stupid 3aboo WIZARD EDITION LOL grognards, start playing BEST EDITION", it had a fucking lot to answer for. Not only in regards to "Okay so we dump our old game that we liked and start afresh, I want X" but also in the sense of "Fine, we'll do as you say and convert our game to 4. How the fuck can we represent anything anyone was ever playing?"
The automatic answer was "A Monk is a 2WF Ranger who just wields his fists! Pretend the magic swords are fists or weeaboo blades! A Druid is just a Cleric of plants or a Feylock! Reflavour the powers to be more tree themed! A Necromancer is just a Wizard, Cleric or Warlock, reflavour them! No you can't have a fucking pet skeleton, that breaks the game. PRETEND ALL THE OTHER PCs ARE YOUR SKELETONS!"
Some people did take the piss, explaining that you could refluff things as completely retarded concepts, or indeed "Sure, X options actually suck dick, so just play (a Laser Cleric or whatever) and reflavour it as (the thing that sucks)!" in an effort to show how stupid it was. And this is justified.
Actually, maybe it's not that 4E is the first game that made such a big deal out of telling you to reflavour everything, more that it's the first game where it was so necessary.