It is definitely subjective. For me it goes back to somebody using the phrase when dissecting trade scenarios. The thesis is that a quarter is an elite player who you can build around. And that dimes are complimentary starting players on playoff teams and nickels are the other NBA starting players.
5 nickels or even 3 dimes don't equal a quarter in a trade. Take Dirk for example, the dude is the epitome of a quarter, whatever nickels and dimes surround him the Mavs are in the hunt. Same goes for Lebron, Duncan, Kobe (unless he's surrounded by pennies lol), Durant. Very few guys are legit quarters. Anthony Davis is looking like a quarter.