When viewed through this lens, the only true balance you can hope for is a soft balance wherein no one feels particularly outshined by another player at the table. Whether 5E has achieved this soft balance is debatable; many argue that this isn't true from 9th level on, 11th or 13th level on, and some more extreme opinions even posit after 5th level (or 1st).
I think this is a false premise. At every table, in every game, one player outshines all the other players in any given session. IMO there has never been a session played in any RAW version of D&D where all players contributed equally. The drivers of this are not class, subclass or level. The primary drivers are the in game choices, dice and adventure design in that order.
1. Choices. A player who makes good choices will contribute more. A player who makes bad choices (whether logically smart or not) will get bad results - the fragile Sorcerer who smartly backs up away from the Orcs at the door and an Ogre comes through a secret passage and kills him. Or an example from play tonight - we knew we need a light shined on a door to open a secret passage and my Wizard figured "what about one of these lit candles on the floor" and when she picked it up Mummys jumped up out of the Sarcophogi and nearly killed one of the PCs in a fight that was "easy". This is before you even consider the stupid choices (or on the other side brilliant choices). Choices drive this more than anything else.
2. An 8 Charisma Barbarian WILL outshine my 18 Charisma Bard in Charisma checks with expertise with good rolls by the former and bad rolls by the latter. Not can outshine, but will outshine.
3. Someone who built a PC to excel at the exploration pillar will probably be outshined when a session is entirely focused on social interactions with a little bit of combat. The things above it on this table (choices, dice) could change that, but rarely will.
Those are the three biggest things that affect one player outshining the others at the table. While mechanics, class design can and do favor or bias the to the benefit of certain classes, the root cause of one player outshining the other at the table are not these things. They are the things listed above are and they are in that order.
More ripple effects come from this. Play culture begins to turn away from creatively using what's at hand to find ways around or over massive challenges to instead using raw mechanics in optimal ways to win against enemies that were designed to be won against. Having encounters where your party is meant to feel powerful is not a bad thing; however, when every encounter is balanced along these lines, it means that players are rarely forced to think outside the box for overcoming challenges.
This is a great point.