There can only be one
Many times over the years I have pointed out to believers that they are almost atheists too. After all they disbelieve in thousands of Gods. All of them except their own.
I imagine that kind of thing was embarrassing because now it has now become fashionable to say that all the Gods are actually the same God with a different name. That Muslims, Hindus and others are doing their best to come to Jesus and that their religions are simply the closest they have managed so far.
There is usually that implication that Christianity is the proper religion, but some Christians will go further and say that they are all equally right. That the one true God is happy to see all those different religions continue on their own paths.
You can see how that could be accepted by people who are only Christian on Sunday anyway. They go to church and sing a song or two. If Muslims sing different songs than so what? It's all the same thing really.
But for real believers this can't work. None of the major religions are compatible. For Christians everything depends on Jesus being the son of God. Whereas Muslims know him as simply a prophet and can't therefore find the crucifixion as significant. Hindus have a multitude of Gods in all shapes and sizes, Native Americans worship animals and pray to the dead while Druids look to Nature and the spirits of tree and stone. For Rastafarians Jesus came again as Emperor Haile Selassie.
Once you say all ways to God are valid then you can't just count the more popular religions. Scientology must be as holy as Christianity. Joseph Smith's golden spectacles viewed with the same reverence as the cross of Jesus. God meant Mormons to have multiple wives just as surely as he meant Hasidic Jews & Sikhs to keep their hair uncut.
If you are not willing to accept Haile Selassie or the Reverend Moon as your saviour then you have to fall back to claiming that all those other religions are fake. That all their devout believers have been misled by wishful thinking or indoctrination. That just having faith is meaningless if you have it in the wrong God.
Then you need simply demonstrate that yours is the right God.