To oversimplify, for a given specific impulse, putting three times the amount of propellant into an engine will result in exactly three times the thrust. Other things, like engine weight and such do not scale directly.

Pressure-fed engines like the lunar module engines have the virtue of great simplicity, since there are no turbopumps. The tradeoff is that they are poor performers compared to pump-fed engines, which generally can run at higher pressures, and for larger systems, propellant tank weight becomes a serious issue. Propellant tanks do not scale directly for a pressure-fed system.

In the lunar module, the engine was both pressure-fed and ran on hypergolic propellants. It had the virtue of being extremely reliable, which was what they were looking for in that application.

I did a lot of work on large, pressure-fed systems. The largest one I have ever seen designed was Truax's Seadragon, which would have been something to see launched. It was built like a ship, rather than a rocket, and would have placed 1.2 million pounds into orbit. For the record, the design weight of the completed International Space Station would be about 1 million pounds.