Good points Pete the “wipe out his enemies” scene was indeed sandwiched immediately before and after shots of Fredo's fishing lessons to Anthony

My take, for what it is worth!

As regards Tom's loyalty, my view, Michael never has to “maneuver Tom into pledging [his] loyalty” at all
Tom's loyalty was a given, beyond reproach irrespective of what Michael did or didn't do and which Michael certainly took for granted too

If I had not misunderstood! your analysis....
I am confused! Why? “Coppola [needed to tell] the audience that Fredo is the real subject of the conversation” whether “Tom was oblivious” or not
Besides Tom, undoubtedly has no say whatsoever in Fredo's fate

We, the audience already know Fredo's time was up with Mama's death, Fredo's fate already sealed, having witnessed the following -

Michael to Fredo
Quote
Fredo, You're nothing to me now You're not a brother, You're not a friend I don't want to know you or what you do
Michael to Neri
Quote
I don't want anything to happen to him [Fredo] while my mother's alive
Michael's chilling kill order look at Neri and Neri's subtle nod, at Mama's funeral