Yes, now, are you going to claim that someone actually took the MLB rulebook, and specifically cut that down to the game your 5-year-old plays? Because I would be dubious of that proposition. If not, then this example is not really relevant.
I submit that the rules of baseball in general are pretty simple, and that the MLB has branched from that and produces Advanced Edition Baseball for Professional League Play, that they have added lots of rules to.
The argument you present here is like claiming OD&D is complicated, using the 3.5e rules as evidence.
I'm not hugely familiar with the rules of baseball, but if they are anything like the laws of soccer, the official rules spend far more time discussing the conditions of play than they do how to play.
For example, in the laws of soccer, the rules describing what is proper footwear to wear when playing soccer are the longest section of the rules, and the rules describing uniforms (including shoes) are longer than all the rest of the rules combined.
Similarly, I strongly suspect that of the 170 pages of rules issued by the MLB chairman, the vast majority are going to describe the requirements of uniforms, the playing surface, the stadium, the ball, the bats, and so forth and not how to play baseball. Likewise, I suspect that a huge percentage of the rules concern the behavior of teams toward each other before and during the game, such as for example that the host has to commit to providing certain medical facilities, certain press facilities, and so forth and that the teams cannot or should not engage in spying on each other and so on and so forth - none of which has to do with playing the game, but which instead has to do with managing professional teams for profit when the players are employees in a union with contractual agreements with the employers.
One of the things that is of great personal interest to me as someone who thinks about RPGs intellectually as a hobby as well as who plays RPGs as a hobby and writes his own RPG rules as a hobby, is that no RPG fully undertakes to describe those processes of play in the same way the laws of soccer or the rules of baseball do, probably because they would be terribly boring, would be ignored in most play as often as they are in the real world, and RPG publishers have no real interest in ensuring uniformity of the play experience in the way that sellers of professional competitive sports do.
Indeed, really only when Indy games came out do I remember anyone trying to describe the process of play in a rigorous way at all, such as defining what a valid proposition was, or defining whether a proposition came before or after the stakes, or before or after the resolution, or before or after the fortune mechanic, whether the fortune is disclosed and/or reviewed and how and to who and in what situations, what situations require or do not require a fortune roll, and on and on and on. And to the extent that prior systems did try to define the process of play, such as the 1e AD&D DMG actually seemed to be trying to do (one of the reasons I think it's been so enduring), I think at the time few people understood (including the writer) what they were actually describing, and how and why those processes of play prevailed at Gygax's table but were not necessarily functional in different situations. I know at the time I didn't, and it took a lot of experience running games and an increase in maturity before things started clicking with me what he was trying to say and why he was saying it.
Every time complexity comes up, I find myself referring back to "The World's Simplest RPG" which I will frequently claim has one rule:
"Whenever a proposition is made, flip a coin. On heads the proposition succeeds, and on tails the proposition fails."
But I'm actually being a bit coy here. While the "The World's Simplest RPG" does have one rule in the since that we normally think of rules, the game actually has a book thick set of meta-rules that are implied, unstated, and left to the individual table. You cannot play the world's simplest RPG without those meta-rules, because those meta-rules tell you want an RPG actually is. All the rules of an RPG actually tell you is how to resolve in game conflicts. People reading the above rule likely usually go, "Ok, I can see how that would let you play an RPG, dysfunctional though it might be.", but in fact they only see that because they have in their head a vast set of rules they don't think about concerning what an RPG is and how one is played. In the same way that kids in a backyard can set up a practical baseball field, and get a game together with some balls, bats, and gloves without having to think about the rules and regulations concerning any of that. They are house ruling or else relying on hidden rules built into the system (such as, "How is a baseball made").
I'm convinced that for any RPG, this hidden rules are at least as complicated as the RPG is, and for a rules light game are often longer than the rules of the game are. And if you've played with different tables, you'll quickly realize that these meta-rules shape the game quite as much as the rules of the game do.
MLB has rules that are so long not because baseball is complicated, but because they've had to write out all the meta-rules (well most of them) that are unspoken or else in a less casual game would be decided by consensus, such as, answers to questions like, "It's raining. Should we quit and go home?"
