Just because 2004-2008 Obama was the most gifted political orator of his generation and Rubio isn't doesn't qualify one over the other.
But I'd say it's a little tough to directly compare the two outside of them both being young and freshmen senators when they were running.
The overall dynamics of the election are much different too.
In 2008, Bush was immensely unpopular. Obama has pretty much hovered in the 40s during his second term with an occasional spike or two into the 50s. In 2008, Obama carried the verbal promise of removing our troops from a dumb, unpopular war and giving health care to everyone. He was young, fresh, exciting to people.
There was the historical prospect of him being the first African American president. And there was also an element of fatigue over another Clinton following a Bush who followed a Clinton who followed a Bush. Obama had some incredibly smart people working for his campaign, while Hillary made more than a few mistakes during the race. Obama was also able to point to her previous support for the war. None of this year's Republicans can say one really supports Obamacare on a large scale. The only thing they've ever even brought up is Kasich accepting the extra Medicaid money for Ohio.
Rubio being the first Hispanic president doesn't quite carry the same weight, especially when most Hispanics are likely to vote Democrat in November anyway. He and others have failed to find a winning strategy against Trump because Trump is such an anomaly who isn't beholden to traditional political rules. All these politicians have all these advisers telling them what to do and say, all the way down to what tie to wear or whether to even wear a tie. Trump couldn't care less about that ****. He could stroll out there in boxers and a wife beater if he wanted to. He didn't get this far in life without some clue of what he's doing.
Obama's rhetoric of hope and change along with his promise to bring the troops home and give health care to all were a nearly unbeatable combination. And the deal was sealed when the economy completely went in the toilet late summer/early fall of that year. McCain had gotten a pretty good bounce out of the convention and was holding his own, but then that happened.
Sure, Republicans hate Obamacare and many don't agree with Obama's foreign policy, but neither of those are as unpopular as the Iraq War was by the time 2008 rolled around. Eight months is an eternity in political elections, so there's no telling what might happen over that span that could tip the election in one direction or another.