People need to realize that even when a development team has 10 people in it, the truly senior ones that can actually work on the hard stuff (networking, performance) are only 2-3 and even then not every single one of them is experienced in every part of the core of the engine, and on top of that if you are updating a networking code you usually can't put 2 people on it, to do it in parallel. The rest of team are usually developers that can do new features but may require a specification or some guidance from the senior people, and then there are 1-2 juniors that can't do anything exciting yet, but can make the bayonet be able to open cans. Software is a complex thing it usually takes half a year for a new person to be able to do anything significant and a great deal of experience with the product to be able to edit one of the core systems. The good thing is that once the more experienced developers are done with the complex stuff they can shoot out new features for the engine several times faster then the regular ones.