I agree, indie is a bit vague. Could be indie pop - Lana del ray , indie rock - Tame Impala , indie dance - Cut Copy..
Dunno what is actually considered rock these days since there is virtually no path to a career as a rock band anymore, that probably partly explains that lack of pure rock in the hottest 100..
I’m 42, i have listened to a lot of JJJ and to be honest I reckon the late 90’s and 2000’s rock/indie stuff was mostly shithouse, I just never got spiderbait/tumbleweed/custard etc. And that stuff was absolutely flogged to death, I only put up with it waiting for the latest Prodigy/Chem Bros etc track to be played.. I feel exactly the same about the 100 in the last decade, mostly full of shit with a handful of great tracks..
I remember someone analysing what style of track historically charted in the top ten and in most cases the chorus/verse had “fuck” in it and/or was some sort of indie folksy BS..