I agree that Lepanto was not a crusade, except in the very loosest definition of the term.
As for the "unimpeachable" sections...
1. Fall of Constantinople 1453 making the exploration of new trade routes possible.
Technically, it had always been possible to explore for new trade routes, but the fall of Constantinople simply made it much more important to do so.
2. The time of the passing from middle ages to early modern age as an era in which there was a spirit for new experiments and approaches to things made possible among other by the invention of the printing press.
This is also true, but it doesn't automatically mean that a ship or fleet will sail west into the Atlantic Ocean. Keep in mind that a similar voyage had already been made when neither conditions 1 nor 2 were in place (Leif Erikson's voyage.)
So basically, you make a good case for the likelihood of someone like Columbus going out there, BUT, it was not the only way things could have turned out. Even if the Ottomans had but concluded a trade deal with the west, # 1 ceases to be a major concern. We also need to consider a # 3, that the Portugese already HAD a route to India that was overseas. In 1488, Bartholomew Dias had sailed around the Cape of Good Hope, thus circumventing Ottoman controlled territory.
In other words, the necessity for getting around the Ottomans was already done. Totally. It must also be remembered that Columbus had a very, very hard time getting people to support his mission. Now, think about that. If so many people were opposed to such an expedition in that time, it must have meant they must have either thought his plans were doomed to failure, were unnecessary, or both.
Of course, Columbus proved them wrong, but the fact that so few people were on board with his plan in his lifetime is indicative of the lack of necessity of crossing the Atlantic in his day. The funny thing was, Columbus's plans were based on a miscalculation:
(from Wikipedia)
"Columbus believed the (incorrect) calculations of Marinus of Tyre, putting the landmass at 225 degrees, leaving only 135 degrees of water. Moreover, Columbus believed that one degree represented a shorter distance on the Earth's surface than was actually the case. Finally, he read maps as if the distances were calculated in Italian miles (1,238 meters). Accepting the length of a degree to be 56⅔ miles, from the writings of Alfraganus, he therefore calculated the circumference of the Earth as 25,255 kilometers at most, and the distance from the Canary Islands to Japan as 3,000 Italian miles (3,700 km, or 2,300 statute miles). Columbus did not realize Alfraganus used the much longer Arabic mile (about 1,830 m)."
"The true circumference of the Earth is about 40,000 km (25,000 mi), a figure established by Eratosthenes in the second century BC and the distance from the Canary Islands to Japan 19,600 km (12,200 mi). No ship that was readily available in the 15th century could carry enough food and fresh water for such a journey. Most European sailors and navigators concluded, probably correctly, that sailors undertaking a westward voyage from Europe to Asia non-stop would die of thirst or starvation long before reaching their destination. Catholic Monarchs, however, having completed an expensive war in the Iberian Peninsula, were desperate for a competitive edge over other European countries in trade with the East Indies. Columbus promised such an advantage."
Funny how history works, isn't it?
