Actually, in point of fact, most of these methods for links are just different perspectives/flavors/variations on the same basic thing. It’s really a question of how deep the connections go, how two way they are.
One big difference with the deity to cleric link vs the familiar link is how “personal” the link is. The familiar link, and the warlock link as you described it are very much a one to one link. The deity links are much more a group link. Much less personal and much more complicated because deities have so many followers and they offload to avatars and there are lots of people in the link Deity<->One or more Avatars<->Maybe High Priests<->Priests<->Worshipers
And the deity links are more fluid. A worshipers mana feeds will change, dynamically, automatically, depending on who the local priest is, etc. So the deity links are vastly more complicated webs (much like the super links required for the city’s Wards vs the Schools wards) than what a warlock’s link would be.