I've gamed with Dungeon Masters who pull your character around by the nose a little bit, but I've never dealt with or witnessed a DM wholesale possessing anyone's character.
That would be... awkward.
I've seen it and lived through it. Wasn't fun.
Heck, the "pull you by your nose" led to one of the worst con expeirences I ever had, where the DM decided that since he knew everyone except me and this one other guy that one of us was going to be the butt of his jokes. Different system, but my Noble Duelist spent the better part of an hour being described in detail how he was dealing with the literal naughty word in the bilge of a ship, just being the butt of all the jokes.
One of only two things I remember from that game. The other being the only time my character got a chance to fight (in a four to five hour game) being against a boss, and him following his code and willing to die to save a kid. A concept that gob-smacked every "regular" at that table, because I guess this was a flashback to a living campaign and they couldn't understand why I was perfectly willing to let my character (who I'd scribbled together just a few hours before) die to have a single cool moment.
Yeah, yikes. I'm def not one of those.
I'd never think you were. But positions have to almost be overstated sometimes on these forums.
The rules for personality and background show you how to play up quintessential fantasy tropes and be rewarded for doing so. I think they're great because they provide guidelines for the basic behaviors that describe a heroic character that feels true to the Dungeons & Dragons brand.
Of course you're not restricted to the characteristics outlined, and of course you shouldn't feel constrained by them, but they do exist for a reason, and as the Dungeon Master it's helpful to collaborate on anything that isn't pre-packaged in the Player's Handbook. Having an alignment, one ideal, one bond, and one flaw written in ink allows the DM to build adventures with your character in mind, and make suggestions whenever the game stalls around ethical quandaries.
I get that they exist for a reason, I just don't think that reason has anything to do with me. I rarely even end up writing them down.
For example, I have a friend who started running a game for us set in a world where the bad guys won. The Evil Overlord took over the world, he's currently fighting the gods who are trying to prevent his ascent to true godhood, and the rest of us are living in his evil empire.
My character is an artificer, and I figured he had two really defining moments to shape his outlook on life. One was a very large man, probably a minotaur, being an abusive bully to people around him when he was a child. Cementing in him that idea that the strong make the rules. The other seeing a smaller person using a pulley system and a lift to raise up something like an engine that that minotaur for all his strength couldn't lift. Power doesn't only come from physical strength, tools can be a path to power. That is why his "virtue name" as a Tielfing is Lyft, to remind him of that moment.
If I had to say he had a flaw... he still thinks he can keep his head down and live a safe life. He's not a coward per se, but he certainly defers and is trying to just keep out of trouble. This is of course impossible considering he is in debt to a mafia and befriending a druid (one of the only groups still fighting the Overlord and therefore basically a terrorist, plus the guy is very much "burn the empire") and a paladin (who are all supposed to be dead, so basically a zombie terrorist).
But, this is enough for me and the DM wasn't really a part of this other than me asking questions like how he saw the society working.
For example, I have enough experience as a DM to know that I should anticipate a high stakes conversation among the players in situations where they've taken a hostage. It's helpful to be able to say "your alignment suggests we can count on you to do the right thing" or "your ideal suggests you believe this person should be treated with dignity and respect" when indecision strikes or infighting ensues.
That's not me taking control of anyone's character, that's me having a tool with which to stoke the fires of inspiration. In my experience, humble though it may be, that has been welcome at the table and leads to a faster-moving game.
I agree with reminding players of their own character traits. I don't use alignment, because it is far too simplistic and contradictory (not getting into the alignment debate here), but if a player is struggling to figure out what their character would do, I see the value in helping to highlight the question.
Your dwarf belongs to the circle of stars and will not wear metal armor for contrived reasons specific to the D&D brand. It's really that simple, but you're free to collaborate with your DM on an approach that works for you. I think star metal sounds awesome!
That bold part is the part that bugs me. It is a contrived reason from an older edition that makes no sense. You might as well say that Monks can't wear blue clothes. If it at least made some sense, it would bother me less, but it doesn't.