For completion, the ultimate idea was what catfoosh said - the more people who have beaten the map, the less points you get for completion. I think that this is a really good idea, and my only concern with it was that shitty maps that nobody likes to play would start getting farmed more because they are worth more than better maps of the same difficulty. Not sure what the perfect solution is but I definitely like a dynamic completion based point system over strict tiers.
I think this could work for maps which are t4 or harder. From memory, I think maps of the same difficulty at these tiers generally have roughly the same number of completions after a few months. e.g littleman, soar and valley (which is much newer) have similar numbers of completions and difficulty (haven't checked, but I think they are roughly around 200?).
There are some exceptions like exilenpals which has like 30 completions even though its t5 whereas a lot of t6 maps have about 80.
For lower tiers, popular/old maps like beef have disproportionate amounts of completions relative to other maps of the same difficulty since they are played a lot more and a lot of these players don't stick around/play all the maps.
What about making more tiers / subtiers? About a year ago I remember someone made a spreadsheet giving each t5/t6 map a more accurate rating (e.g pharaoh would get something like a 5.7 to reflect it being harder than iT which could get a 5.1). Idk if anyone still has the link to that.
Keep completion points and tiers, but get rid of top ten. Instead, wr will have the same amount of points, and all places beneath it will have points based on the time difference between them and the wr. So if you are 2nd place by 10s you will get less points than someone who is 2nd place by 0.1s.
I'm not sure how well this would work in reality. Being 30 secs off WR on beef is not that great whereas being 30 secs off WR on pharaoh might get you 2nd or 3rd place. Even if you considered the difference as a % it wouldn't work either (e.g being twice as slow as WR on beef is awful but being twice as slow as WR on pharaoh is still pretty amazing.)
I prefer the % or exponential decrease systems suggested.
Some other games specify certain time bands (which are unique for every map) you can come in to get more points. However, that looks like a lot of effort and it might have to constantly be updated as new strats are found.