Futures is essentially on par with top D1 schools, give or take. That means they hover around 6.5. And there is a pretty big difference in futures and top pros. Futures are more likely to break down, use faulty strategy, be overeager, and a bunch of other problems. Yes, it's all mental (which is why once Federer got over it he went from top player to untouchable status), but there are still other aspects to it.
Ryan Sweeting beat Taylor Dent (granted Dent is old and came out of retirement) and although he gave Sam Query a decent run, he was getting killed. He was holding games, but the difference in abilities was clear, and it was just a matter of time before Sweeting broke down and Query would win the set. Sweeting could hit the ball very hard and serve well, but his percentages were horrible. Shots that would be routine winners for most top pros he missed wide. His service percentage was around 30-40% (I think closer to 30). He was able to get away with that on futures and challengers, but not in an ATP event.
There IS a difference between futures, challengers, ATP, Masters Series, and major events. The difference is mental in addition to difference in either power or consistency.
Top pros can consistently play well, day in and day out. They know how to win (or most of them do), they rarely have a bad day, and their average quality of play is much higher than challengers events players. Getting hot is stupid to base how good you are. That's like saying a 5.0 who got the hottest he ever got can take Federer to a tiebreak (though that's taking it quite extremely). If Federer got hot for a few certain matches, he'd have 2 calender slams, and the record for highest winning percentage in a season. Sampras got hot and won the 1990 US Open. But after that, he wasn't playing close to that level for another 2 or 3 years!
Futures are not equivalent to division 1 college tennis. Futures is a higher level. The top div 1 players have rankings hovering around 800-1000 whereas the top seeds in a futures tournament will generally be around 250-300, with a ranking cut off of 800-1000. So only the very top college players even make it into the draw.
All players play futures beginning their careers. Every single one including all of the current top 10.
When a pro takes the leap from futures and challengers, its not because they have improved their game significantly in the space of a year or so, its because they have put it all together mentally.
Ryan sweeting. In that match yeah he was missing easy balls. Why do you think that was? Why do you think he broke down? Is it because his ground strokes are technically not up to scratch?
Its far more likely that he 'broke down' and started missing easy balls because he wasn't mentally as tough or mentally as prepared as Dent.
Lets look at Federer. In 2003 he broke through and won his first slam, and then in 2004 he won 3 out of the 4 slams and was world no.1 the entire year. Was Federer of 2003 a technically inferior player to Federer of 2004?
Again the difference was purely mental. Its amazing what a strong dose of confidence can do for a player.
Your right that regular tour players play more consistently day in day out when compared to futures players. You know why? Its because they are stronger mentally. Not because they have technically superior skills.
All those things you mentioned, strategy, breaking down, being over eager, they're mental skills.
Of course there is a difference between playing grand slams and playing futures, its just not as massive as some seem to think it is.
People seem to think of futures players as hacks, guys with incomplete games. Sometimes thats true but there are far more who have all the tools, all the shots, but just cant put it together on a daily basis.
Power and consistency are great tools to have as a player but there's only 1 thing that ALL top 100 tennis pro's have in common, and that's that they are incredibly mentally strong, driven and determined. The only exceptions are with players who are very naturally gifted like Gulbis, Safin etc.