Actually, interestingly enough, you're all working under the same thought process: That Magus did not want to save Crono. What if he did want to save him? Magus has the personality type of a bitter and taciturn old soldier, so hides his feelings behind a wall of insults. You will notice that the only person he holds in high enough esteem to not do that to is his sister Schala. Everyone else he cuts down with words. It is very literally impossible to be around somebody or a group of people such as Crono & Crew without having some of their natural good cheer and high spirits rub off on you and even further impossible to not start caring for them. Especially if you're still holding on to some part of the good side of your soul, which Magus is by pursuing his cause to bring Schala back to him.
You're also working under the idea that Magus missed his chance up there on Death Peak. Who's to say that that one Egg was all that Gaspar had created? Also, you're forgetting that if Schala were to be pulled out at that time, then the rest of the Crono crew would never made it back to safety, including Magus, which would make for a time paradox that would ultimately wipe out Janus and Crono and Crew and then Schala herself for being saved in such a way. Because you have to imagine that if she was pulled out by Magus in the future, she would not have been able to teleport him to safety, which would mean that he wouldn't be able to save her, yet he did. Kind of confusing when you think about it.
I'm sure these are all thoughts that flowed through his mind at the time and afterward. He probably thought it was a safe bet to continue on with Crono and Crew to defeat Lavos at that point and then, if that did not return Schala to him, he would figure it out after that point. He had already spent most his life to that point building his will towards Lavos' defeat. Who knows, he might have even tried pursuing the Time Egg thing on his own afterward, though how he would manage to get to Gaspar without the gates and Epoch, is anyone's guess.
I think this fits the most, especially when you consider that Mystics/Demons put each other down all the time and are quite derogatory. This is their type of friendship, how they treat their friends, etc., if Mystics had friends, which one has to assume that they did. And, like the infamous relationship in DBZ between Vegita and Goku, it could be a competition thing. Magus got beat by Crono and may want a rematch later on, though never says. Or, he may have been saying what he thought. He would probably say the same about himself if he were to fight Lavos and fell beneath its might. He told the truth to Frog and nothing more. "He fell because he was weak." I can not picture this being said hatefully, but thoughtfully. After all, Magus also attacked Lavos and failed, and if Crono fell, too, having already beaten Magus; Magus at that point would be speculating on how powerful Lavos really is, to beat the person who beat him.
He would definitely have to respect Lavos' power after that and it may have been his goal TO have Crono resurrected for that purpose. I mean, if your power failed and his power failed, and you know that you two are the strongest there is, it would be a pretty safe guess that it would take your combined power and then some to bring down the bigger foe.
Magus is very intelligent, very calculating, and patient to a fault. I don't think that he fully understood the capacity of the Time Egg, and was suitably impressed by it, but I don't believe he spent much time resenting Crono for being saved and not Schala, given the facts I listed above.
