If lightning network includes tech that can support billions of transactions, can it be used without bitcoin? Why not use lighting with an uncongested coin?
Yes, any coin that has segwit or a comparable fix for malleability can use lightning. Litecoin is already supported. You can even have atomic swaps between both over lightning channels.
Bitcoin is the most popular with the most resources behind it, so it makes sense to leverage off it. There's nothing stopping similar networks occurring on other coins.