Any single piece of evidence in isolation should always be doubted. That's basic critical thinking: Don't treat anything as fact without independent corroboration.
And what does being head of Starfleet have to do with it anyway? As recent events in the United States and the UK have reminded us, leadership does not guarantee special intelligence, infallible insight, or even basic competence. Power often ends up in the hands of fools. If anything, the litany of Starfleet admirals and Federation officials in Trek history should demonstrate that quite well.
Heck, maybe Marcus doesn't even know the history of those ships in the models. Maybe he just ordered some subordinate to set up a bunch of ship models in his office because he thought it was the sort of thing the head of Starfleet should have on display.