Champion mastery VS other game modes & bots.
I believe, since the current system gauges basic mastery of champions; and because it grants 0 -> 300 points on defeat vs 700 -> 1500 points on victory.
It should grant a low amount of points in other game modes, especially bot games since new players /should/ go there to give new champions an initial test. I see no harm of granting up to 300 points max on victory, to milk efficeny and motivation out of the system it should be applied wherever it induces positive, meaningful incentives. [ here is where I don't think ARAM games should grant more than 200 points max given the environment type VS it's meaning to champion mastery if the system was to be applied there ]
Tl;dr champion mastery should give incentive to new players trying champs in bot games for a start, other modes may need further analysis.