It's a different solution to the same problem of scalability. Also, if "Monero lightning implementation" has problems, you have another coin that could offer a solution. The use case for Masari would be similar to that of Monero since they are both privacy coins. As for the idea that this is a Monero knockoff, you could have said the same thing to Monero as it was a fork of Bytecoin. Monero added to the cryptospace by adding new technologies and answers to problems. In this way, Masari is following in the footsteps of Monero since it will also add new solutions to problems e.g. uncle mining, WHM algo, block tree sharding, fully client side web wallet, etc. Masari also plans on having a benevolent relationship with Monero and in this way it wants to add to the cryptospace. Monero could choose to implement out fixes/solutions or it could choose not to. Since Monero is a bigger ecosystem, it might be a little harder to do get consensus so that is something worth considering. Masari on the other hand has a smaller group of devs and so it can move quicker to innovate and add things.

If you have any more questions LMK.