Not sure I'd describe it as plenty. There are indeed shared passenger and luggage areas next to the double doors in each carriage, where in theory luggage has priority, but in practice if that area is already filled with people then you're squeezing in as best you can as it's just space on the floor - so you can't just put a spinner there unattended, for example. That said, countless people manage to transport large luggage on the Underground every day of the year, so it's far from difficult.