Frankly, I can see no reasonable explanation for the Christian church to grow out of that era if Jesus wasn't resurrected. His ministry was a mere 3 years before he was executed by the Romans. He preached an unpopular message and his followers were almost exclusively lower class and illiterate. Yet somehow out of that has come Christianity.
It's true that the Jews weren't evangelistic with their beliefs except among fellow Jews, but there were the religions of the Greeks and Romans that were, in the sense that they had the support of those in power and were even in a position to impose their religion on others. That's where the power was.
The Roman Empire was a positive hotbed of alternative religions. For starters, the Romans as a matter of policy did not impose their pantheon on their subject peoples, so there were plenty of religions to choose from.
In addition, the Romans and Greeks themselves converted to other religions. They would adopt the Syrian rites, for example, or they would Judaize --- these latter were the so-called "god-fearers", who would give us the name "Timothy". The centurion Cornelius in Acts 10 is an example of such a man, as presumably was St Timothy prior to his conversion to Christianity.
Then there were the "mystery religions" such as Orphism and Mithraism.
And then there were the various religions that grew out of Greek philosophy --- Stoicism, Neo-Platonism, and Epicureanism.
In common with Christianity, they had something to offer the
individual worshiper,
personally, that was lacking in the state religion.
What was
different about Christianity was that it succeeded in
becoming the state religion, a position from which it successfully suppressed the alternatives. As you put it: "They had the support of those in power and were even in a position to impose their religion on others. That's where the power was."
We can only speculate on what would have happened had Christianity been allowed to stand or fall on its own merits.