I'd like to make your sentence more fair:
Would Christinaty be as successful being the only single religion that doesn't offer any kind of eternity reward ?
The reward of eternity is in fact the standard for religion, from Egypt and Greece to current religions, even sometime in indirect/distinct form (reincarnation in buddhism or hinduism thats leads to nirvana). In fact most of them offer something pretty similar to heaven, call it Valhalla, Jannah, Nirvana.
And as far as I know for most famous religions, all of them offer extreme and infinite punishement for breaking some rules. All of them answer for fears and interrogations about life after death, not just yours, but for your family, friend or love.
And it's not by accident. Because that's not just a trick of one or a few religions, like a convenient way to make people believe in one perticular religion, that's more deeply one of the most important points of a religion, and in fact for a God to be.
It's really beyond imagination to think what should or should not do and think God, but I still can't imagine Him existing, sharing is existence in the form of a religion and to just let everyone of us rot forgotten after death, including beloved, believing and honnest ones.
So that's pretty clear Christianity would not be successful, but not just because of bad settings in the reward system, but for not making any sense (and be the only one not to).
I don't believe myself nor in God nor in Heaven, but let be fair to say Heaven is not just about success, and not a main reason for Christianity success as other relgion offers just as much or even more on this point.
