Previously, this wasn't true.
It was an objective problem because too many levels meant too many
pointless levels; by "pointless", I mean a level where nothing happened.
No talent.
No skill.
No unlock.
The game was simply bloated badly by levels that technically did nothing for your character, other than increasing their numerical standard by a completely trivial amount. This problem ended up being more pronounced in things like professions, where 800 levels worth simply means a huge grind with an awful lot of waste.
Another significant problem was how quickly players out-levelled zones and had to either do green/grey quests, or move on halfway through a story. This is a problem because it breaks immersion, and effectively makes zones irrelevant as self-contained (yet sometimes continuous stories). Related to this, the power jumps between expansion points made for a wholly uneven experience on the way up. What this meant was that level x8 was hugely lucrative in next-expansion content, and horribly inefficient in current-expansion content.
So, until recently, it was a clear case for: Yes. A level squish was an objectively good idea. It wasn't just a number, it was something that was having an adverse effect on the game.
7.3.whatever, of course, made some relevant changes to levelling flow by nerfing heirlooms, slowing levelling down a little, and scaling zones so that you can't out-level them and feel like you need to move on. These are good changes, made especially good by dynamically updating characters that are of dissimilar level obtaining similar experience as a percentage. Friends with toons at different levels can suddenly play together and, speaking as a beneficiary of the system, it's amazing. The expansion roll-ups was also a good idea, meaning that you didn't have to rampage through old content as fast as you could, in expansions that, quite bizarrely, were behind the current old-world timeline.
But the changes do nothing about the sheer volume of dead levels, the needless profession grind, running out-of-timeline content, and gear-to-expansion break points.
For that reason alone, there's an objective value in a level squish; but it would need to be accompanied by other changes, such as level retuning in the old world and a rework of how expansion content works. There's also the small matter of the effort it would take, but the re-scaling that was done recently didn't even need a major patch... Suggesting that an expansion-level development cycle could easily fit it in.
Sadly, none of this will persuade those who are against it "Just because". Similar to the item squish, those self-same people are likely to caterwaul that they've been playing for years and don't want to suddenly feel weaker. The snag, of course, is that those very same people will also argue that 110 or 120 is "just a number".
And we're back to the quote.