Fusion faces massive challenges, but neither of these are showstoppers.

Laser-induced fusion isn't a realistic prospect for power generation at the moment because those big lasers aren't very efficient. It's still worth doing because there's a lot of interesting physics we can explore in those labs. Magnetic fusion doesn't suffer from wall-plug efficiency issues so much, and is a more realistic option for an economically viable reactor.

Scientists are probably quite blasé about efficiency calculations because, once you reach ignition, increasing Q to the value you need isn't so difficult (certainly easier than getting to Q=1 in the first place).

Regarding tritium availability, every tokamak power plant design features a tritium-breeding blanket made of lithium. This is not trivial, but it's by no means the biggest technical challenge faced by magnetic fusion devices. These tend to be related to plasma stability issues and surface heat loads on the inner walls of the reactor.