Lets ignore the Trinity for a moment. Instead, I’d like to focus on the very nature of who both faiths refer to as “Heavenly Father”.
Mormons believe that “Heavenly Father” (aka “Elohim”) was once a normal human, who had a god father and goddess mother. Elohim then ascended to godhood, becoming who they refer to as “Heavenly Father”.
You too can become a god or goddess. If I understand things correctly, if you perform certain ordinances, live in a certain , and have a temple sealed marriage, you can become god or goddess. Upon becoming a god (with the possibility of having multiple goddess wives), you too can rule over your own planet (or universe?), and have a plethora of spirit children. Those spirit children then begin to gain physical bodies themselves, and begin their journey to godhood. Which is why this moves beyond tritheism and into outright paganism.
If you’re wondering where the starting point for this progression is, there’s isn’t one. Mormons believe in infinite progression, not an unmoved mover or uncaused cause. Elohim does not exist beyond time. When approached about Aristotle or Aquinas, thus far no Mormon has been able to present an answer to me or my wife.
To quote my wife; “my goal for eternal life is to worship, not to be worshiped”. Which is the opposite of Mormonism; where the end goal is specifically designed for men to become gods, and to be worshiped themselves.
To be frank; the Mormon “Heavenly Father” is not the Christian God. Unless you can reconcile these extreme differences, I cannot see how Mormon baptisms are remotely Christian, nor can I see how Mormons can be identified as Christians in general.