For some people strength relative to their own weight is more important than absolute strength.
The ideal amount of may muscle differ between these two goals. For absolute strength, more muscle mass is always better. For relative strength, there are diminishing returns, and assuming symmetrical gains, perhaps within human reach a critical point at which more muscle is detrimental to performance.
The ideal amount of muscle mass for relative strength is more than zero obviously, and appears to be higher than the amount a beginner carries. It may however be lower than that of e.g. a bodybuilder, who by conventional wisdom is weaker in bodyweight movements such as pull-ups, than a lighter but still muscular person.
At least two important factors are involved:
1) the less muscle mass you carry, the larger the discrepancy between percentual increase of muscle mass and percentual increase of total body mass (the proportion of your body mass that is muscle increases, as muscle mass increases). This factor causes you to become stronger relative to your bodyweight as muscle mass increases.
2) power is proportional to the square of the cross-section of muscle, weight is proportional to the cube. This factor causes you to become weaker relative to your bodyweight as muscle mass increases.
At some point, factor 2 will outweigh factor 1 and additional muscle mass will reduce relative strength.
relative strength (Sr) = absolute strength (Sa) / total mass (mt)
Sa = cross-section radius (r) ^2
mt = r^3 plus non-muscle mass (mn)
Sr = r^2 / (r^3 plus mn), a concave function in [0, inf), Sr reaches its maximum for some finite value of r
A third factor which I excluded is the mechanical disadvantage that may come with large values of r. It will only come to play if Srmax is close to the upper limits of attainable muscle mass.
The optimal r for relative strength will differ between body types and height. Question is, does it fall within the range naturally reachable, or not? I.e. is there is a situation where an athlete would prefer to not gain any more muscle mass, even if it resulted in higher absolute strength? And if so, at what level of muscle mass (perhaps reasonably expressed as FFMI and assuming a fixed body fat percentage) would that most likely happen, for a certain height?
More specifically, did any of you experience an increase of muscle mass, without raising your body fat percentage, which improved your absolute strength but reduced your relative strength, and if so, at what level? Among those you know that are strongest in relation to their bodyweight, what is the typical FFMI?