1) I'm almost sure that Squall survived Ultimecia/Edea's attack at the end of disc one, because she cured him(Ulti wanted Seifer to interrogate the party's leader(Squall) about the real purpose of SeeD).

2) Cloud NEVER was a normal person, even before Nibelheim. In Before Crisis, he defeat the Ravens of Avalanche, who were in the same power level of SOLDIERs.
Cloud didn't join SOLDIER only because he was mentally weak.
So the fact he defeated Sephiroth at Nibelheim, is proof of his strength, not of Sephiroth's weakness.
Not to mention that... It was a coward attack from behind.



In my opinion, SOLDIER have more chances, because they have the advantage of numbers(all of those Genesis-copies from CC, were SOLDIERs in the past), and in training(they have their own version of the Danger Room(from the X-Men) at level 49 of the Shinra Building).
And SeeDs are augmented only with GFs, while SOLDIERs are augmented with Mako AND Jenova-cells.