Three DMGs and two PHs* adds up to a fair chunk o' paper; and it was all explicitly called out as being core.
* - or was it two-and-three? I only got the first PH-DMG-MM set and lost track after that.
Two DMGs. The second is optional and focused on higher-level play (e.g. Paragon tier, levels 11-20). Three PHBs.
Note what "core" means in 4e: because in 4e,
everything 1st party is core. Literally every WotC-published thing is.
That doesn't mean you have to USE it, though I would certainly recommend using the original books, with some of the more-important errata (like to Stealth stuff and skill challenge math...and it's worth noting that people ripped into 4e for needing errata to the Stealth rules.....only for 5e to then need errata to
its Stealth rules, and getting even more such errata in 5.5e!)
"Everything is core", in 4e, means that everything is held to the same balance standards. Everything. Supplements? Expected to remain within the approximate balance range of the first three books. Magazines? Same deal. Miniatures tie-in products?
Same deal. "Everything is core" means the creators legitimately committed to making it so EVERYTHING published for 4e could be trusted to stay pretty much fine, so you didn't need to review everything with a fine-toothed comb for possible crappy exploits. This doesn't mean NOTHING unbalanced snuck through! A few things did. (As an example, the "Windrise Ports" background was initially OP, within the bounds of 4e balance, but it was later redesigned to be, if anything, on the weak-ish side. Compared to 3e, of course, nothing 4e ever produced was even
remotely overpowered, but that's a separate concern.)
If you didn't have anyone playing a Monk or other Psionic class, you really didn't need PHB3. If you didn't have anyone playing a Barbarian or Druid or Sorcerer etc., you didn't need PHB2. Sure, there might be something useful in those books, but useful =/= necessary.
Sorry, "Golden Wyvern Adept" doesn't ring any bells.
(edit - typo)
When 4e was still getting the finishing touches before going to the printers, WotC did an early reveal where they showed off some actual mechanics, not just high-level ideas or setting materials (which they also did with other stuff). One of the things they previewed was a feat called "Golden Wyvern Adept", which included both some mechanical effects I can't recall, and a little bit of relatively mild story/RP context (you have been initiated into a group called the Golden Wyverns, who were a group of spellcasters, possibly Wizards specifically[?], that had certain goals and expectations).
The community response at the time was
VEHEMENT OUTRAGE. Fans absolutely
skewered the 4e devs for having the unmitigated GALL to
presume the story for anyone's character, for
forcing in-character actions or affiliations in order to do a particular thing. This taught the devs an early lesson: Don't force anything in RP. Let RP exist completely on its own, so mechanics can be used for whatever flavor and story the player wishes.
And guess what 4e was then pilloried over? (Something I, personally, mocked 4e for because an ex-friend poisoned the well!)
Flavorless mechanics that didn't include any story or roleplay elements!!!
Yes. It was
very literally the playerbase being completely unpleasable. The very same people who brought out the proverbial torches and pitchforks because of the Golden Wyvern Adept feat "enforced" setting elements or whatever...who then slammed the 4e we eventually got for
NOT containing those very elements.
It's one of the most obviously infuriating examples of how 4e literally
could not win, an encapsulation of how 4e was subjected to "heads I win, tails you lose" expectations.