I've just read about the battle and couldn't understand some things.
Why did Bonaparte think he would be able to capture Arcole easily from such a disadvantageous position? And why, after Austrians managed to stop Augereau's attack on the bridge with just three battalions, his objectives for the next day were the same? Jomini explains that forces were kept in the marshes because outnumbered French couldn't risk fighting the Austrians in the plains, which contradicts the whole plan of marching up to Villanova.
Was it feasible for Austrians to send their main forces across Adige at Zevio on the 16th and capture Ronco, as French main forces were held on the northern bank?
In all, I still don't understand how Austrians managed to perform so weakly in this battle. Outnumbering the French, not only they failed to defend the eastern bank of Alpon, but they seem to have half of their forces beaten by Massena alone, while the other half saw no action at all.
There's a few things here, and I will try to tackle them based on my memory, so if someone catches and error, my apologies.
I'll answer the first question last. The reason the Austrians fought in such a disorganized manner is that the army at Arcole was 1. divided into two wings and 2. was a hodge-podge of other units thrown together to lift the siege at Mantua. They had already failed to do so, and were desperate to push passed Napoleon and get to the city. Poor communication between the two wings due to distance and the FOW is the reason they weren't more effective.
Second question, was it feasible? Yes, in fact the original plan had been to use a pontoon bridge to ferry the Austrian army across the river. Again, it was an army without a unified command structure and that wasn't talking to its various parts well. It was simply a missed opportunity, common in war.
As to the first, this is my speculation, but its based on Napoleon's patterns and the situation as he saw it at the time. Bonaparte was never fully aware of the size of the Austrian army until after the battle was over. The Austrians went out of their way to hide the amount of men they had available, which was part of the reason the French lost several skirmishes in the days leading up to Arcole.
Another reason Napoleon thought it was feasible, was because he was Napoleon. While he wasn't yet the celebrated general he would become, he never sat on the defensive. His was always on the offensive, regardless of the situation. He preferred to make the enemy respond to him than the other way around. Up until that point, he had met with success when attacking the Austrians and throwing them on the defensive. The objectives didn't change because the battlefield wasn't overly large and control of the field hadn;t changed.
Also keep in mind that Massena wasn;t committed until the 3rd day of the battle and Bonaparte knew he was nearby and marching to the battle. Should the French have lost the battle? Yes, but the same can be said of most of Napoleon's battles if you're going off of numerical superority. It was rare the French outnumbered their enemies. It was luck and balls that won the day for the French.