No, he's got weak stats to make up for the fact that he never has to run up to opponents to use physical attacks. He can burn through an ATB gauge and start charging again faster, so they made him weaker to balance it. He also has a ton of native HP, even surpassive Fang I think, who has Sentinel natively, so that's where a lot of his stats went. I dropped +250 strength on him with accessories and didn't even need to bother with defense because he's so tanky already.
It's not so much deus ex machina as non sequitur. A few times in the final sequences the characters just decided to charge in and beat the stuff out of everything that moved in a given area with absolutely no justification and even in some cases a lot of indicators that it would have an effect directly contrary to their goals.
It's a little like a nuclear reactor overloading, and the heroes charging in and punching the fuel rods deeper into the reactor until the reactor goes critical, then the problem disappears and everyone lives happily ever after. A deus ex machina is where something is so completely implausible and unhinted-at until this point that it comes off as a lazy way to end a story, but it technically makes sense if you are determined to just go with it. In our example, if there was an earthquake at the last second and the ractor fell into the ocean, cooling the reactor and preventing an explosion, that would be a deus ex machina. FF13's ending does not qualify as deus ex machina because it didn't make any sense at all on several levels simultaneously. It's deep how many contradictions in logic there were.