Not sure if this helps at all, but @Silvia Bluejay and I were lucky enough to interview Marcus Miller for BGM in 2018.
Strangely enough, we asked him pretty specifically about his involvement with the Sire range, and how he saw it fitting in to the market.
Marcus was quite clear on this ... he wanted to ensure that there was A BASS FOR BEGINNERS that didn't require those beginners to cut corners on quality and playability; he wanted to produce the sort of bass that he would have bought when he was starting out, if only it had then been available.
@Mudpup has this about as right as right can be.
PS: He really does wear that hat all the time.
PPS: I mean Marcus Miller, not Mudpup.