Are these mining pools cheating us?

I am mining with one of the top pools – 2… I am seeing that the mined coin count daily is dipping every day recently.. like 10-15-20% compared to prev day. It makes me suspect that there is something fishy here.. because I expect to see ~ same number of coins mined everyday..

Do you also see such a trend?

Also, which is the transparent & reliable pool to get into for RVN?