Bismillahi Al-Rahmani Al-Rahim
The question here revolves around a ruling in the Hanbali madhhab that â€œit is unlawful to lead in a mosque before its assigned imam except with his permission or by his excuse. (b: If he is late and the time becomes short, they pray.)â€ (Zad al-mustaqni`, c6.2).
I do not see where this alone is enough to presume anything about who the imam will be. The mu'addhin may know something that you don't (seeing the imam through the window, know that the imam was already there and would come in upon hearing the iqamah, hearing the imam's car, etc...).
In the West (particularly in my town) there are many cases where people arrange their breaks so they can attend the group prayer. It is the imam who serves the community, and not the community who serves the imam. If the imam is late, the group is justified in praying without him. If the imam is frequently late he should realize the disservice he is doing to the community and remove himself from this responsibility. Fiqh is knowing that the afterlife is more important than this one.
And Allah knows best.
Wa al-salamu `alaykum,