How can people at low levels like 25 to 30 be earning 800 points after only a couple days play?

When you start the game in the beginning, the scenes are easy to open (it take fewer plays), so you can easily complete some of the HW cases, such as find clues, open star boxes, find compasses, find and use materials, level up, and travel to a new chapter. Low level players are usually restricted by their low energy stocks, which can be overcome in a good generous team. If they have learned Magic Eye technique for Spot Diff competition, they can easily earn that many league points.

It is also possible those players are second (or higher) accounts of an experienced player, who knows how to strategize the HW cases. But I'd expect them to focus league points on their primary account.