Do you really believe that 1) anyone coming to Ferrari will be given the chance to match Alonso and 2) that Alonso will automatically beat anyone that drives alongside him? Of course, the debate here will always be: did he beat the other because he has No. 1 status or because he's actually quicker, especially when he's a successful established driver there.
The only thing any driver going alongside Alonso has to achieve is matching his laptimes in the short term and then beat them in the middle term. While matching Alonsos consistency and/or throw him off balance with his performances. Then that new driver will become de-facto no.1 and Alonso would have to deal with it.
Would that be a tough task? You bet! And why should it be any other way? What you seem to demand, however, is Ferrari giving proven worse drivers than Alonso strict equal treatment. That makes no sense, and it won't happen. Do you really believe, even with super-equality, Massa would be capable of more than stealing valuable points from Alonso every 10th or so race, while overall never getting even close to beat him in the WDC? From what I've seen over the last years, that would be the "best" Massa could ever hope for.
I think Alonso learned from what happened at McLaren in 2007 and a No. 1 status must have been part of the negotiations with Ferrari at some point. When he was at McLaren he clearly said that he was surprised that a 2 x WDC did not get No. 1 status, even worse, over a rookie and the fact that he looked at Ferrari, a team that had come from a recent history of No. 1, No. 2 status, and brought Santander backing when he came on board, is telling.
The bolded doesn't make much sense, given that Massa was allowed to race Alonso for the first half of 2010. And for that we even have evidence, not just what you think.... If Alonso had negotiated no.1 status in his contract that wouldn't have happened.
I think one of the reasons Massa is doing so poorly is that he's not the type of driver they need. He was clearly the teams' favourite son before FA came on board. He was close to winning a WDC and he outperformed Kimi, a recognized fast driver, for a season. He expected equal treatment no matter what. Ferrari must find someone new enough or someone desperate enough to return to F1, that is willing to play second fiddle but still perform at or close to the max. (Sutil, Alg...), or a driver that has no hopes of winning a WDC and sees F1 as an office job for Ferrari (Kova, Glock?).
Well, exactly. Massa had it all laid out for him at the start of 2010. He knew the team, the style of car Ferrari builds, had beaten their last champion for 1.5 years. Yet still Alonso outperformed him very quickly and since the gap has only grown. The simple truth is, Massa can't match, let alone beat Alonso for any length of time. Once in a blue moon, yes, but every other driver on the grid (well, maybe not Narain) could do that to every top driver.
In a nutshell: Alonso is a distinctively better F1 driver than Massa, and he's using that advantage to full effect. What else do you expect?