I noticed that your region is Hong Kong, which means that I seem to be able to communicate with you in the language I am better。
If all people knew that there was no afterlife then they would just focus on the pleasures of the present world, what you are saying is ridiculous, first of all the example you gave is not appropriate, it could be argued that this is something that simply could not happen, maybe you are trying to get me to imagine a world where no one is religious, but I can't imagine it, there are other forms of religion that can fill people's hearts and souls, and people will still do things like worship, the People do need faith, and Christianity is one of the biggest. Secondly, and this is the most ridiculous point, I would laugh even louder if you think that people who don't go to church spend their Sundays trying to give to their communities and families, if people don't go to church and don't have a faith their minds are only focused on the world, just look at the young people in South Korea and Japan, they aren't religious, but can you say that their lifestyles are any more fulfilling than those who are devoutly religious? (At least the religious people don't watch porn at home until they die).
Also, what you call “meaningful” is a very subjective term. What does meaningful mean? It makes mean to atheism to attack Christians online and in reality, but what about other people who are not part of your group? Can you decide for them what is meaningful?
Let me summarize for you, first of all, what you call “meaningful things” are only meaningful in the sense that you think they are meaningful, and secondly, what you're saying is purely not about solving problems because the examples you give are inappropriate and uninspiring, and what you're saying is just about venting your subjective feelings, whereas I'm going to say that I hope that others to talk about the impact of Christianity on the world at large (preferably on a political level). Not for you to talk about the impact of Christianity on one person, I know you are asking about the world as a whole as well, but what you are actually asking is a personal question, and as we all know, some people will move on to more meaningful things (the ones you believe in), some will stop there, and some will get stuck in the muck, it's up to the individual.
So you didn't solve my question, I didn't say that Christianity is just better for the world, why else would I have come to ask? All I'm saying is that your rhetorical question doesn't solve my question.