No catapults. They don’t “need that boost” because they are generally smaller and lighter (and lighter-armed/equipped) aircraft. I remember when some Chinese media complained that the J-15 was a “flopping fish” because it couldn’t be loaded up with a full load of fuel and weapons and get off the deck of the carrier.
The Su-33 weighs 40,000+ pounds and it uses ski-jump with no catapult, and the Super Hornet weighs 33,000+ pounds and has to use catapults.
(That was just a quick Google search, so maybe not very accurate data, but the Chinese jets aboard these carriers don’t seem any lighter than their American counterparts)
Edit: OK, I see about the fuel, but even then the fuel and weapons load added in, even half-so, seems that it would not make a jet like the Su-33 any significantly lighter than American carrier jets.
I don’t have any particular naval air expertise, so it’s entirely possible I’m wrong. From STOBAR - Wikipedia
That bit - “the aircraft may be required to limit its weaponry and fuel package in order to reduce the launch weight of the aircraft” - was pretty much the exact criticism of the J-15, IIRC.
Just looking at the F-35, the C variant carries more fuel and weapons than the B variant