As others have explained, it has flawed but there's this so called solution - Lightning Network. I advise you to read all about it. When you say bitcoin becomes irrelevant what are your basis? The price? Like going to 0? Or people finding other coins to used either as payment method or SoV (store of value)?

I'm assuming that you're looking at the price for you basis if so then bitcoin would be still be relevant because there's no other coin that even get close to what the price of bitcoin has reached so far. On the contrary it might just be the beginning, the price drop that we witnessed in the past week might be a good indication that the bullish cycle might come to an end and 2019-2020 will the year when the bulls started to get control of the ecosystem again.