If Doom came into battle with nothing more than his standard battle armor and didn't specifically prep for Banner's anti-tech devices, and Banner didn't specifically prep for Doom but already had effective tech dampers in place, all this shows is that Banner is close enough to Doom in intellect to take the occasional unprepped bout in a tech war and that his anti-tech field is effective enough to work against Doom's standard armor, which, granted is HUGE but doesn't mean he is above Doom.
I don't think it even means that he would win a majority against Doom in this kind of bout, just that he can win it if the circumstances are right.
A good comparison to my mind are some of the wins Iron Man has managed against the Hulk. While it seems like his best bets against the Hulk would be massive amounts of prep, and that he would be pretty outmatched in a straight up brawl, his most convincing wins have been toe-to-toe with help from environmental factors (that he is smart enough to utilize). In fact, conversely, prep hasn't always helped him much.
Another factor here is that the Hulk doesn't have the one-on-one wins to directly balance the scale. If you look at the win ratio between the two in hand-to-hand solo battles and don't factor in anything else, it would look like Iron Man is probably the Hulk's superior in raw power in a straight up fight. While I am sure there are people who do think this to be the case, I'm pretty sure they're solidly in the minority.
If you look at the Hulk's performance against mutual opponents or against large groups of heroes including Iron Man (among whom Iron Man is arguably not even the most powerful), among other factors, it is easy to conclude that the Hulk is above Iron Man in terms of raw power but that Iron Man is tough enough to make it a fight and to even win one now and then. But those now and thens are what we have mostly seen in non-draw single fights between them.
We have the common practice of estimating win ratios here on the Board, as in, I think the Thing would beat the Rhino 7 or 8/10. Now let's say we will only see one conclusive fight between the two in an actual comic, and it's one of the 2 0r 3/10 that the Rhino would win. Doesn't mean the ratio is wrong, just that we've seen an example of the minority win.
A brown belt will often beat a black belt in a tournament; the black belt is officially recognized as a level above the brown belt, but it's still possible for the brown belt to win, perhaps even if it the only time the two of them fight.
Any fight that hinges on fighting skill, tech smarts, strategic smarts or even mystical skill can go either way pretty easily unless the two opponents are totally mismatched. A wrong initial step from one opponent or a brilliant one from the other can set the tone for the whole fight and start momentum that can't be reversed.
All that said, we don't even know if Banner wins this from the post.
Everytime you see Ironman KO Hulk they go out of their way to show the Underdog-ness of it. Now I would be happy with them showing Banner pulling out his TV remote, and give atleast some lip service to the idea that he's competing with an equal.
The casual dismissal, is the problem. "You can't beat me with your machines i'm smarter than that" That isn't a compitition between equals its one party showing contempt for the other parties capability. . . Sure we can play it off as just in character talk, but if the writer wanted to be respectful, and not just stroking his current character fetish, he could have done better.