Look, I don't think Riddle/Voldemort is especially well-written, but this isn't why. Him taking over Malfoy Manor and everything that went with it was one of the most interesting aspects of his character, and the best insight we get into him.
Riddle calls himself Lord Voldemort. Lord. This is a man who comes from the utmost poverty - being an orphan in England in the first half of the 20th century is as far down the ladder of this classist society as you can get. The title of Lord is something that, traditionally and societally, is conferred by a monarch and passed down through familial lineage. Riddle, however, just takes it and uses it. And those who follow him accept this. It's a test of how far he can push boundaries and the people who fall for his charisma.
He doesn't just invent a persona, he assigns it status and power in a clear and direct way. People call him Lord Voldemort without questioning how he got that title, out of fear, despite the fact that he still has nothing. He uses the Lestranges' vault at Gringott's because he doesn't have one of his own. He uses his hereditary connection to Salazar Slytherin, and ignores the squalor he saw when he met the last of the Gaunts. He has no wealth, no status, and although in British social hierarchies breeding is as important as wealth, if not more*, he has neither, because growing up in an orphanage doesn't prepare you for life among the ruling class. But he doesn't need these things, because he can invent them or take others'.
*Wealth, titles, land ownership - these are all important aspects of being part of the British ruling class. If someone from that class loses money, they may lose status, but not necessarily respect, because their behavior, manners, and social conduct all indicate that they've had "good breeding." History is rife with British gentry forming alliances through marriages to save themselves from debt or poverty, because if one has good breeding, they can hide their loss of wealth. Someone who gains wealth without being born into the ruling class, however, doesn't have the hallmarks of "good breeding", and therefore will be considered as less-than by those in the upper class, even if their wealth is more substantial. Therefore it matters just as much whether Riddle came from "good breeding" as what his social status is. The Gaunts, for example, had lost their generational wealth several generations earlier, but what was more significant about them was their lack of good breeding, which is what cemented the end of the nobility of their lineage.
When Voldemort takes over Malfoy Manor, he's asserting the farce that is his self-given title of Lord and challenging the Death Eaters to question him, knowing they won't. It's also a very overt way for the author (boo, hiss) to show that everything about him is constructed and a facade. All he has, all he is, he takes and imposes by force. As OP said, so much more aptly and succinctly than me: "Like many dictators and leaders of criminal organizations Tom doesnât feel he needs to buy things to have them and instead simply uses force to take what he wants from other people."
What greater show of power, than to bend an entire social hierarchy to your will and make a mockery of it while also asserting it? What better way to assert leadership than to restructure an entire society using force and people's fear of you to do it? Isn't that what all fascist regimes do? In a book series rife with poorly researched parallels and a disdain for learning about history, Voldemort taking over Malfoy Manor is one of the few examples of a solid allegory of modern era fascist rulers. Then, for good measure, Voldemort also takes Lucius Malfoy's wand, an act of emasculation not just in the symbolic act of stripping him of a crucial, and personal phallic object; as the patriarch who shares the name of his stately home, Malfoy is stripped of power completely, both as master of his own house, and of the use of his wand which was his greatest weapon and protection. Voldemort ensures that Malfoy can't retaliate or try to take his home back, because he understands the significance of the relationship between a wand and the wizard it has chosen, and that any other wand Malfoy might procure will never serve him as well as his own did.
He controls a puppet government from a seat he took by force, under a title he gave himself. He is, very literally, a self-made man. Every aspect of the scene in Malfoy Manor at the start of Deathly Hallows is written to reflect his relationship to power and how he uses it. The way he says,âYaxley. Snape... You are very nearly late." If they aren't late, then they're on time, yet his phrasing implies disapproval. It also carries a subtle threat in his choice of words: "late" has connotations with the deceased, not just timeliness, so there's an implication that his disapproval has severe consequences. We know this about him already, but it's driven home by the scene laid out to the reader: Voldemort says this as Professor Burbage's limp body floats over the table, then proceeds to tell Snape and Yaxley where to sit, conferring status on both in the process, and then gets down to the business of managing his puppet government.
Only when he's finished imposing his will on all those present and beyond, and taken Lucius Malfoy's wand, does he revive Professor Burbage, doing so in order for everyone to witness her fear and desperation before he kills her in cold blood and feeds her to his snake in front of the whole table. This is also an act of asserting his power - she dies when he decides she will, not a moment sooner, and he's showing that he has no reservations about any suffering or torture he causes leading up to that moment. It's a deliberate warning to all those witnessing it, and a chilling reminder of his capacity for dehumanizing and destroying others. All while sitting at the head of it in a seat he took by force, under a name he gave himself.
He's at the mercy of the Malfoys? He's at the mercy of no one, except his own fears - and everyone around him pays for those fears, not him.
