So... I'm curious.
Does this mantra hold to games like Palladium Fantasy or Rifts?
I'm not convinced smaller is necessarily better. I'm not against mega-books, though reading them can be tedious if you like to hold them and read for long periods. To me, Good is Good. If the book is 4-inches thick but it's damn good, well... it's damn good. I don't expect my players to own anything other than dice. The onus is on me as the GM to run the games I want to run, and thus, I resort back to my rule: good is good.
Another consideration is that many of these heavyweight monstrosities are PHB's/DMG's/MM's all rolled into one. So you're probably getting bang for the buck. If that's not a consideration then are we just talking about fatshaming (LOL) the girth of our dead-tree slabs?
Big Thick Books of Glorious Power I Own - FantasyCraft, Talislanta 4e (The Big Blue is literally what everyone calls it and is by fair margin the favorite edition), Palladium *anything* (on the plus side they're paperback, on the minus they're paperback). Most of the Wod20th anniversary books are necessarily massive. FFG Star Wars core books (and they have a lot of overlap in rules - so that takes a hit in value).
I'm not going to dismiss a game simply for the presentation. I'm the type of consumer that walks around a product a *lot* before I purchase. I kick the tires and check the oil, and measure and poke and prod before I hand over gold. Size is a secondary concern to me.
Conversely - I'm a Savage Worlds fan. Their books are very very slim. Take Savage Worlds Rifts, while they do a great job of giving you high-level details of the Rifts setting, because of space reasons, they miss a lot of the juicy juicy details in the Palladium sourcebooks they draw from. The tone feels "lighter" in touch because of it. While that might be a good thing for some, I think in a setting-by-setting case those details can matter for a GM.
From a player perspective? I don't care - because even the best written setting books will only get presented to the best ability of their GM. For me, generally, less is more. BUT... having the full-assault of a verbose writer, while tedious at times, can give you deeper insight as a GM into intent of setting conceits - which you're free to discard - in terms of how you want to present it to your players.
TL/DR Fatshaming your fatass books shouldn't be the issue. The content is king.