I am not sure I agree. The suffix -miş (and 4 other similar forms because of vowel harmony) is first and foremost indicative of time (the past). Yes there is the mood aspect, but time aspect, IMO, is primary.
From the book "Turkish, a Comprehensive Grammar":
The markers of past tense in Turkish are the verbal suffixes -DI and -mIş and the copular marker -(y)DI. "the past copula -(y)DI expresses past tense in absolute terms; that is, it locates a situation in a time prior to the moment of speech. -mIş, by contrast, is a marker of relative past tense."
Robert Underhills "Turkish Grammar" calls it Narrative past tense.
Geoffrey Lewis "Turkish Grammar" writes "the mis-past is exclusively a past tense" " miş-past. This base is formed by adding -miş to the stem: gelmiş, görmüş, almış, bulmuş. Two distinct functions are combined in it."