Like it or not, people who went to prayer house or religious gatherings socialise more than people who stay indoor and only interact with limited amount of people.

While this statement is true, its also true even if you're not religious. I was not raised religious at all but always got together with family/cousins/friends nearly every weekend.

... they tend to be happier considering the fact human are social animal and the feeling of loneliness due to lack of human to human interaction is the build-in alarm system to warn us against solitude. It’s this reason religion is so success because it’s enforce togetherness and make you feels like you’re part of something.

Kinda. This study [0] of 3,942 19-year-old in Sweden put it best:

... religion and religiousness per se have little impact on happiness. In particular, we find that social networks tend to be positively associated with happiness, and that this effect is driven by co-organizational membership among friends.

So while religious upbringing can force people to socialize, that doesn't mean the lack of religiosity will have a negative impact as the lack of religion does not dictate that you will not congregate/gather with peers/friends/family and feel the same level of "belonging" to a group - even if its not a well defined group.

If we’re going into a utopian world where human doesn’t need to work anymore and social security is guaranteed, religious will be something even bigger than today.

I'd say this claim is unfounded. Why must we turn to religion? There are clubs, groups, meetups, friends, events and niches of never ending categories that easily fulfill the need of "belonging" to a group - it's actually one thing humans are really good at - forming "in" and "out" groups.

Source: [0] https://www.researchgate.net/publication/275143707_Faith_or_Social_Foci_Happiness_Religion_and_Social_Networks_in_Sweden