Remember that twin-engined aircraft such as the 777 must be able to complete a take-off once the aircraft has reached the V1 speed even if one engine fails. V2 (also calls Talke-off Safety Speed) is calculated for each take-off and is determined by factors including the aircraft's take-off weight, wind speed and direction. V1 (also called Take-off Decision Speed) is the speed below which the take-off roll can be safely aborted and the aircraft come to a complete stop before the end of the runway, and includes factors such as the available runway length.
So, the engines must each have enough reserve thrust individually to be able to continue the take-off after V1 has been exceeded, and for a short runway, that can be quite a bit below V2 and Vr (rotation speed).
The biggest of the 777 engines, the GE90-115 has been tested beyond 115,000lb thrust and is sufficient to maintain cruise of a 747 with just one power plan operating. GE owns a 747 they use for a test bed for their engines and they strapped a 90-115 to this aircraft for their airnborn test program. In this config they ran the other three normal 747 engines at flight idle power and used the 777 engine to maintain flight.
So on a 777, in normal conditions with both engines providing thrust, there is little need to get anywhere near full thrust capability, even for a max weight take-off.