From what i heard you say, it sounds like “feed and fuse from commons” means to ditch your current legendary penguin, and then feed and fuse commons to uncommons, then uncommons to rare, then fuse two rares with max 1st level and 2nd level to make a legendary pet with levels 70,70,0? then feed that all the way to level 90,90,0 and fuse it with mini polaris to get a divine.
If this is indeed what you are asking, I would keep the penguin. Its second ablility is level 69, so im sure the fame cost for increasing it to level 70 is much lower than the fame cost for feeding and fusing two rares (let alone all the way up from commons) to get a legendary pet with second level 70. So I suggest keep with the penguin.