That's nice summary :) But I would change something:
I also think, that you should take into account all maps made by each mapmaker.
About "Using all maps penalises map makers who have more, but some not very high quality maps.", Isn't that's why you added this "T" factor? With walue of 3 for map nr 10, overall rating is not affected by bad maps too much.
Also I'm not sure if making "T" fixed is ok. It penalises map makers, who focus on quality instead of quantity. So someone, who made 5 good maps (let's say rated 4,3), can have lower score, than someone, who made 2-3 good maps, and 7-8 average.
like:
1st person: 4,3*25+4,3*18+4,3*14+4,3*10+4,3*8=32,2
2nd person: 4,5*25+4,4*18+3,8*14+3,8*10+3,7*8+3,7*7+3,65*6+3,6*5+3,55*4+3,5*3=40,3
(Let's omit "S" factor for this purpose assuming all maps are rated 1000 times or so)
So my suggestion is to use following weighted factor:

where n - no of maps someone made, i - ordinal number
Explanation for ppl who are not in Statisticians clan:
if someone made 1 map T=1
with 2 maps, T1=2/3 T2=1/3 (1+2=3)
3 maps: T1=3/6 T2=2/6 T3=1/6 (1+2+3=6)
(...)
10 maps: T1=10/55 T2=9/55 T3=8/55 (...) T10=1/55 (1+2+3+4+5+6+7+8+9+10=55)
The problem is with "effective gathering data" I guess, so you can limit it to for example 10 maps per person.
Also yes, it means, that someone, who made 1 map with highest rating will be 1st on your list, but hey, try to make only 1 map, that will be masterpiece :)
Edited 11/17/2014 18:54:38