Is an oligopoly that isn't a cartel problematic? If the lightbulb manufacturers jack up their prices, how long can that last until new incumbents come around an

Is an oligopoly that isn't a cartel problematic? If the lightbulb manufacturers jack up their prices, how long can that last until new incumbents come around and compete margins away? You know what people hate more than oligopolies? High prices. Consolidation is not de facto problematic. Unless said consolidation leads to cartel-like behavior or entrenching regulations (which even Adam Smith recognized as a problem and a propensity of elites, I'm not arguing in favor of laissez-faire capitalism), margins will be cyclical in a free market and colluding oligopolies will eventually face new incumbents, because high margins attracts competition and investments. There are exceptions like markets where cost is prohibitive for new participants, say telecom (hello Rogers-Bell-Telus), but I don't see how that applies to lightbulbs in the 21st century.