No, it doesn't imply that only an alien invasion would have been only thing sufficient to draw Clark out as Superman. It doesn't imply anything. What you're basically doing is engaging in fallacious thinking that most closely resembles this
fallacy.
HYPOTHESIS CONTRARY TO FACT: This fallacy consists of offering a poorly supported claim about what might have happened in the past or future if circumstances or conditions were other than they actually were or are. The fallacy also involves treating hypothetical situations as if they were fact.
Clark's saves here and there indicate that he's doing what Jor-El spoke of in regards to flying: pushing his limits. With Lois, he pushed hardest because she knew who he was on the base and saw his face all while being a world famous reporter. Notice how before Zod even invaded, Lois was on the cusp of publishing his story, even coming to his home and asking him to let her do so.
Jonathan's attitude was only ever about readiness. He repeatedly said, and I've repeatedly quoted to you, he could envision Clark standing proud in front of the human race someday in a way that would change the world. He just urged caution to his son when he was a child, and as soon as Clark wasn't a child anymore Jonathan was more open to Clark finding his own way. Before he died he admitted to a teenage Clark who was just declaring how he wanted to "do something useful with [his] life" that he may have reached his limits, saying "Clark has a point. We're not [his] parents. But we've been doing the best we can. And we've been making this up as we go along, so maybe...Maybe our best isn't good enough anymore."
It's not fair or accurate to claim that Jonathan didn't want his son to be a hero or become someone like Superman one day, and it's illogical and pointless to suggest that Clark would have remained forever hidden had Zod not invaded; there are too many possible variables and permutations to claim that as fact.