The way I see the runes or the original Glorantha and RuneQuest is as follows. Which is similar to what you say, but perhaps subtly different.
The runes formed the strength's of a character by what a character did, who (gods/spirits, allies, cults, nations, etc...) they did it for, and the character's association with particular rune 'elements'. I did not see the runes a some token magic item; but more of a definition of a hero and its association to the game world through it's actions and choices. A character gained status in cults (or as an individual), completed quests/adventures for some (rune oriented) cause, and through their relation with the runes/aspects/elements, developed power and influence which were augmented by that association. Characters who associated and were allied with opposing runes were usually (not always) the 'enemy'. Power status is achieved within the sphere of several runes with the benefits that the allied status and associations provided.
Therefore, I see that the runes were (are) a core part of the game (mainly from a Gloranthan perspective), and a strong and ever present component that shaped and defined a character by the character's influence, allies and direct manipulation by association of rune 'elements'.
In addition to "power by association", the runes also helped provide back story and character definition the closer a character became involved in a rune's sphere. Think of examples (in RQ2 and CoP) that use Ruric, and how he changed from a 'neutral' nobody to a full on Yelmalion Light Lord.
The 'runes' are strongly present in the play of the game (RQ2), and sometimes deeper than many might be aware of, without the need to be a simple to comprehend 'physical' or tangible item.