I just don't understand what prevents you from getting a mostly mundane item with minor magical qualities or being chosen to be knighted in literally any system ever. Like...those things are things that can happen in essentially all fantasy games.
It can happen. That doesn't mean it is well rewarded or well supported.
For example, taking the Leadership feat and having an army of followers in 3rd Edition sounds like a cool idea. However, I very quickly learned that the army of followers gained is virtually useless against any kind of threat I might face. Instead, I was better off having the followers act more like a NASCAR pit crew working to support my PC by churning out magic items and stuff like that. Powerful? Potentially. The experience I wanted? Not even close.
As for being a knight... again, you can do it. But having a horse and being mounted (something which should be a positive) very quickly became a liability. The horse likely isn't surviving even minor spellcasting on the part of an enemy.
If I'm playing in a game built around the expectations of common attack magic and wirefu combat, that's a very different set of assumptions about how the game works works and how I'll interact with that as a player.
Another example that relates to a species/race thread is something as simple as whether or not a dragonborn has a tail. That could be something which is just fluff and aesthetic like it is in D&D, or that could mean I have an appendage with which to make attacks (or be targeted by them).
That's just looking at combat.
How does the world work?
Am I expected to have magic items or a fantastical beast as a mount for my character to function properly? That changes what I buy and how the economy works.
Some games don't have levels at all, so there isn't an expectation of wealth or items.
Are flying creatures common? Teleporting?
How I would go about building a castle and where I would put it is different.
What about social interactions? Am I dealing with the a-hole version of changelings I mentioned a few pages ago? Does a DM (or game) rule that Charm effects ate just good vibes toward a person or is it essentially mind control?
How those pieces are handled change the game and my interactions with it.