I tend to think of this topic as what's the function of a skill system?
A skill system creates subtle variations in prospects of success for different sorts of PC builds, depending on the fictional details of (i) the situation and (ii) the player's action declaration for their PC.
In the case of games like RuneQuest, Burning Wheel and Torchbearer, the system also creates a feedback loop into PC advancement/development.
So varying the skill system generates different play experiences. A system with many and varied skills, like Rolemaster or RQ or BW, encourages a focus on minute details of situations and action declarations. In play, this creates a "grittier" experience. Minutiae matter.
A system based on a small number of broadly-described attributes (like say Agon - each PC is rated in Arts & Oration, Craft & Reason, Blood & Valour, and Resolve & Spirit) makes the general fit between these PC descriptors and the described action salient, while making minute details of the fictional situation less important.
In both approaches, it is important that players are expected to have the freedom to describe what their PCs do, and how they approach situations, just choosing how to bring their PC skills to bear. If the focus in a RPG is on the players being expected to follow the GM's lead on what sort of action declarations are appropriate (eg as per some module-based/AP-based play) then skill systems seem rather pointless to me, or even potentially unfair, because they will simply create a "gate" between PC build choices and prospect of succeeding at the GM's adventure.