With enough people in once place, Starlink will suffer from congestion just like a cellular network. I don't think it's fundamentally different in that regard. But great for boats indeed!
It's even worse than a cellular network. With a cell network, one can just build more towers in a particular city.
With LEO satellites, the only way to get more coverage over a particular city is to get more coverage over the entire world.
Half a million satellites ought to be enough for anybody.
I mean, they're planning their own internet satellite constellations. None of them are anywhere close to the 12k satellites in the original Starlink proposal. If you added everyone else's proposals together, you might make 1 more Starlink, but probably not.