I don't think Spider-Man should be the leader of the Avengers. I think that actually should be Rhodes who also should be in the movie.
It should not be Rhodes, either. I notice some toss out candidates for Avengers leader in the era of Wilson as Captain America, yet had no problems accepting a recently resuscitated Steve Rogers being picked to be the Avengers' leader during that phase. If anything, Wilson has more modern-day experience (at the point of stepping into a leadership position) as a superhero (blended with his work in the military ), as he's of this era and did not have to play catch-up like Rogers, yet here we go with just about anyone offered up as the new Avengers leader other than Wilson's Captain America.
But Spider-Man should be the main protagonist. IMO the the heart of the movie should be him dealing with this Stark Variant.
Why? One of the weakest part of the MCU's version of Spider-Man was reducing him to some teen sidekick, running around yelling
"Mister Stark!" with hardly any of the self-reliance (and none of the sense of sacrifice) of the original character from
The Amazing Spider-Man comic book. No one needs to see yet another film with Spidey-Lad and his hero-worship issues about the dead Tony Stark or some variant.
I'm not sure exactly if he is a Stark variant but I do think he will have some connection to Stark, thus explaining why he looks like Stark.
What you're saying is just do write anything to drag Stark back into the MCU. Doom is not Stark, and for his 1st appearance in the MCU, he should be a distinct character, not some variant of a dead man.
but I do think he will have some connection to Stark, thus explaining why he looks like Stark.
Unnecessary, unless you believe moviegoers are so simple-minded that they need a forced connection to explain why the same actor portrays different characters in a series. As distinctive as the late Charles Gray was in appearance, no moviegoer needed 1971's James Bond film
Diamonds Are Forever to justify why Gray's Blofeld resembled Gray's Dikko Henderson from 1967's Bond entry
You Only Live Twice. The reason is that audience of that period were mature enough to accept actors appearing more than once in a series as different characters having no connection. It was not a problem in the Bond example, and it will not be a problem with RDJ's Dr. Doom.