There is one major similarity between the Old Cyrillic and Greek alphabets: originally, both were (mostly) phonemic, but several of the distinct sounds represented by different letters merged later on, so that there was two or more ways of representing the same phoneme with different letters. So the letter Yat seems to have originally represented /æ/; its sound merged with /e/ in Russian, so that /e/ was written as both <Ѣ> and <е>.
In the same way, Greek for instance, used to have different pronunciations for <ω> and <ο>, /ɔː/ and /o/; Greek lost its quantity and quality distinctions, so to this day there are two ways of writing /o/: <ω> and <ο>.
On the other hand, the two different ways of writing /i/ in Old Cyrillic, <и> and <і>, were not comparable to Greek—they were inherited from Greek, where <η> and <ι> had already merged in pronunciation. Old Russian orthography had worked out rules for when to use one and when to use the other (Dotted I (Cyrillic) – Wikipedia); but those rules were artificial:
In the early Cyrillic alphabet, there was little or no distinction between the Cyrillic letter i (И и), derived from the Greek letter eta, and the soft-dotted letter i. They both remained in the alphabetical repertoire since they represented different numbers in the Cyrillic numeral system, eight and ten, respectively. They are, therefore, sometimes referred to as octal I and decimal I.