I don't think they were calling their players toddlers. They were making an analogy.
Many players want to feel like they've earned a victory, but they also want lots of cool powerful stuff. Many of them don't give thought to game balance, they take what advantages they can get so that they have a better chance of winning fights, not losing.
They don't realize that it's tough to be on the other side of the table, making encounters that are challenging without being murderous, or cake-walks that they have no problem with.
I have a couple players that have made optimized characters, and later on said "oh wow this is busted, I'm overshadowing the rest of the party" or "can we tone down this class? It's ridiculously good." Those players end up having more sensitivity to the matter going forward- but they're not every player.
Your position is far more nuanced and reasonable compared to theirs. But also, I think there are some obvious things being stated or mistated.
For Example, I remember a guy years ago who was complaining that they wanted to run a survival heavy campaign. They told their party they wanted to run a survival heavy campaign where camping and supplies would be important. The players then showed up with goodberry, create food and water, leomund's tiny hut, and other spells designed to solve the problems he was planning on them facing. The individual was furious, because the game was designed to ruin all of his plans! Except... was it? The game was designed to give the players tools to solve problems, and when he said "we are going to be facing these problems" the player's built to solve those problems. Because obviously.
The same thing happens when you tell players "I am going to run a campaign focused on defeating undead" you will get characters who are specialized in taking out undead.
Where things get misstated though, is on the part of the designers. Quickleaf seems convinced that the designers are creating all these things "without limits, risk, or real challenge" that they have given no thought whatsoever at how it affects the game if the Rogue can trip enemies at-will.... but they did. They did think about that. They just don't see the Rogue being able to trip or poison people as a problem for the DM. They aren't thinking "well, now the rogue can trip and poison enemies, so now my enemies won't be effective in combat, oh no, this is horrible!" they are thinking "We've given the rogue the ability to help their team by tripping and poisoning an enemy, this is a great tool."
I've also noticed a few other things, for example, many DMs who get on complaining that fights are too easy go with something like "I took the standard pit fiend from the MM, put it solo against a party using all the optional rules and optimal builds, and they defeated it easily!" Well... yeah. The designers never assumed that the Pit Fiend would be solo. They never assumed you wouldn't do something simply like give it magical gear, feats, or increase its health if you were using all the optional and optimal builds in the game. Of course you are going to curb-stomp it. This isn't because the designers put zero thought into designing the game, but because they had different assumptions that you (general) are ignoring. Like never having a solo encounter. Like making sure you have five or six fights before the last encounter of the day.
Yes, players are often not considering the game balance when they make their characters, this is true. But that doesn't mean the designers also didn't consider it, they just set different parameters than you did. And you (general) need to understand that if you are going to fully realize the situation