There's nothing wrong with the server-side hit registration. Higher pinged players do not cause hit registration to become any less accurate nor does anyone have an advantage (except during extreme lag). People who state these things are either ignorant or arrogant.
The actual problem is miscalculations in client-side prediction which can occur in some situations. For instance, one such situation is when you're dink'd/shot in the face and you survive. When this occurs, your cross hair will jump and your shot distribution pattern will change. However, due to delays in networking, your client will register your bullets pre-dink'd, and this isn't accurate with reality. These miscalculations are one of the reasons an aimbot cannot possibly obtain headshots which are truly accurate 100% of the time, although it can obtain them pretty consistently. The aimbot can only knows as much as your client, and your client isn't entirely up-to-date.
These graphical issues become more apparent when either server-side fps drops or while playing with higher pinged players. This is due to a greater delay in the packets, which consequently force your client to rely on prediction for a longer duration of time. The server will intentionally buffer a shot until the higher pinged player updates the server or until it hits some arbitrary timeout. This timeout means players will have an advantage over extremely laggy players.
After the higher-pinged player finally updates the server, it will then play back the gunfire in order to determine which player killed the other first before updating both clients. These delays mean you can get around a corner via client-side prediction before the server finally steps in and says, nope you're actually dead way over here. The client didn't actually shoot you around the corner; you were dead long before that.
If the particular player had lower ping, your client would've been informed of the death far quicker, resulting in client-side miscalculations being less noticeable. There's really only two other nuisances caused by these delays/miscalculations: 1). People using excessive ammunition on players already dead. 2). People seeing a blood splatter on someone's face but then dying.
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