there’s absolutely nothing wrong with allowing the engine to run with settings current hardware can’t handle

Sure, there’s nothing inherently wrong with that, but if you want your product to sell and be successful, the period shortly after release date is where most of your sales will happen. If nobody can run your game at that time, you could lose 90% of the lifetime sales you’re likely to make. It would make more sense to release a slightly pared-down version of the game that actually runs well now and improve it in the short-to-medium term with updates. Or, alternatively, release it when it can actually run well on commonly-used hardware.