The error here, is that you apparently have no perspective which would allow you to appreciate that the Citizens of Heaven (saints and angels) have very high giftedness, which is still finite, and still always radically less than God's infinite capacity. You see no gradations, no differences. Many, many creatures can have dramatically more capacities than I do, and be much more spiritually gifted, and not be divine, just as an angel can have more powers and abilities than I do, without being divine.
Please reflect in the fact that omniscience, omnipresence, and infinity indicate an entirely different order of being, far above that of the creature. There is no comparison between what a saint, or angel, or archangel can do, and what God can do. Even if, say, Michael the Archangel can go from one end of the Universe to the other at the speed of thought, that does not make him divine. He would reject that with terrifying force: "Who is like God?"
Therefore I can say Mary, or Abraham, or even my guardian angel, can hear us from heaven, without saying these holy people are divine. Divine they are not. Servants they are. Gifted they are. God has done great things for them, holy is His Name.
Second, my dear brother, you said "Supposedly, Lazarus does not need to be sent, since he is always mystically present with every Catholic believer, per your tagline."
Is that what the tagline means toyou? Really? Can you not even acknowledge that it's a quote from the Book of Romans and no just some trifle of Mrs. Don-o's? What does this verse mean to you?
This is a perfectly valid point and one "GPH" seems to be missing but I'd also like to point to an even more basic point, one I believe should, at least for any open-minded lurker, make it clear that the "ability" to hear "simultaneous" prayers does not necessarily imply "omnipresence and/or "omnipotence"
Those two terms are reserved for what God can and does do "on earth" (or more broadly, in our universe). Our universe constrained and defined by linear time. (As an aside, I feel its important to note, no one says the saints come down to earth AND ALSO interact with ALL humanity at once here, on earth.)
Those "in" heaven are not so constrained. That's because heaven is not really a place (or other dimension, or any other physically definable entity or space), it's really a state of being. A state of being where one is literally outside of time (or more precisely outside the constraints of time).
So given this notion of heaven, it can be "easily" seen, if one dwells on that concept a bit (the concept of being outside of time) how it could be infinitely easy to receive all the prayers directed toward oneself "while in" heaven.
To put it in a very simple way, if one has an infinite amount of time to receive even a google plex of prayers, it's entirely possible because even for such a large set of prayers, given an infinite amount of time to both hear and answer them, it would be pretty much like hearing only one prayer for all eternity.
Just sit back and think about it, with an open mind willing to admit alternate possibilities. And you will see that not only what I wrote above is true, but also that what I wrote above does not require omni-anything on the part of the saint in question, since it's not occurring on earth (or any physical dimension), but rather "in" heaven (or in the state of being called heaven).