Strength and Dexterity are quite balanced. It is just not that obvious. If you take heavy armor into account, the only thing left for dex based chars is better initiative and better ranged options. In melee strength is better as it allows for more combat maneuvers. During exploration strength has important associated checks. Climbing, opening doors. Int may need some help though. My fix: Int helps learning things during downtime.
Well, that arguement aside, what I was really getting at is that while Elf and Dwarf and most others were designed in such a way that you can play just about any class and receive a meaningful benefit-- i.e. with Elfs, if you are a fighter than getting those martial proficiencies doesn't mean anything and if you are a spell-caster than one more cantrip doesn't generally help you as much it does a non-spellcaster and if you are a Dwarf, then if you choose to be a warrior, cleric or paladin then the armor profiency doesn't help you much and the extra hit points are of marginal benefit (getting 1 extra hit point means a lot more to someone who is getting only 4 per a level otherwise than one who is getting 8) and your martial proficiencies are wasted, but if you are anything else-- then you aren't as mobile as anyone else and the fact that heavy armor doesn't reduce it further does nothing for you.
Half-Orc is the stand-out example where literally everything the race gives you kind of drives you to be a Barbarian, Fighter or Paladin.. possibly Cleric... and if you choose any other class then you'd be better off choosing any other race. In fact, since previous editions even Monk has been taken off your options list as it has been transformed into an entirely Dex-based class... and doing Ranger is very iffy as it too is designed as a completely Dex based class. (Seriously, that whole "Dexterity is balanced with Strength" argument is one to have because I see Dexterity being handed absolutely all the benefits). Granted, at least your bonus critical ability and your ability to get back into battle benefit somewhat if you are one of those two you aren't nearly as bad off as if you chose literally any other class in the book... to which you just flat-out suck if you are a Half-Orc.
Unless you are going to come back with some what in which a big strength boost and coupled with increased criticals in melee combat only somehow makes you an amazing Sorcerer, Warlock or Wizard.
So although many races have been well designed so that it really doesn't matter what your class is so much because every class can benefit to a good degree by the racial abilities if not the attribute... half-orc is the exception.
And I have a feeling we'll see a lot more of those exceptions once Volo's guide to monsters as I have a feeling the Firbolg is going to end up being capable of only being effective as a Barbarian and Goblins will probably be so entirely geared towards being Rogues that there will be dangerously subpar as anything else.
TheHobgoblin - While I agree that the half-orc is built with a melee fighter strongly in mind, it still won't hurt you to play a half-orc wizard or thief or whatever. The game math only assumes that you take +2 in your primary attack stat. After that everything you do to optimize makes the game easier from the baseline combat assumptions. I have a 9th level gnome sorcerer/warlock who still only has a 14 in Cha and don't have any issues with combat effectiveness or feel I'm underpowered in the party. And the extra int comes in very handy with the social and exploration pillars.
Would a half-orc wizard be suboptimal? I don't know... In early levels have a bit more HP and the ability to stay up for another round after getting dropped to 0 sounds pretty good, and with 16 Con, 14 Int and 14 Dex and 13 Str as your starting stats, you could take weapon master at 4th to start wielding a great axe with some power, getting the advantage of the critical bump.
Okay, well-- that is a different approach. My approach is
"the difference in power level between the person who chose the 'ideal' race/class combo and the person who rolled them up randomly won't be very much and may be nearly incidental even without pulling weird build tricks"-- to me that is balance.
If instead you are saying that balance is that the assumed opponents from the monster manual are going to lose to PCs but not overwhelmingly so even against optimal PCs... that's a different definition of balance...
But, if you have the later and not the former, that means that any player who "knows what they are doing" is going to cake-walk through all supposedly "balanced" encounters.