The affect of increasing bullet diameter in the same case allows the base to be exposed to more pressure. That increases the amount of kinetic energy it "absorbs" and puts more power downrange. It also expends it more quickly because of more frontal area and potentially less efficient shape. The heavier bullet is also affected by drop to more significant degree, delivering less effective range. Friction and gravity overcome it earlier.
There is no "superior" in choosing the ballistics of a bullet - you pick the one that dynamically meets the taskings for that job, in range, impact, penetration, etc. Given equal barrel lengths and bullet weights, the .30x.223 will generally have less range and more power than 6.8SSPC, and that cartridge will generally have less range and more power than 6.5G. That is a generalization, it will get picked to death by fanboys, but the harsh reality is that when you baseline performance factors like barrel, weight, and OAL of the cartridge, you get that.
Whatever, understand what the cartridges OPTIMUM application is, and don't make more of it than it is. It can either do the job well, or just do the job - nothing morally wrong with middle of the pack performance - but it CANNOT be the answer to all applications. It WILL run short at one end or the other of it's power curve, and another cartridge exists to easily better it.
Go fanbois all over it and claim "superiority," and a true appreciation of what it can really do will get buried in a rising tide of nitpicking. No cartridge is "superior," it just has more power or speed at a certain time in it's flight, and might offer some advantages in logistic outside it's ballistic envelope. Performance is purchased in dollars, what one shooter decides for himself is his business.
