Well that's another thing indeed. Even if some genius would invent (much) faster blockchain technology some day in the future, then most shops still wouldn't want to use it due to the volatility. If you're on online shop and your margin is 3%, are you going to accept payments that can easily be worth 10-20% less at the end of the day? That would just be insane.
If those merchants started to accept it the volatility would disappear because they would be able to pay their suppliers in BTC to get stuff that they've just sold for BTC, so the coins would never end up on an exchange and would not affect the value of BTC vs fiat in the merchant's country. The exchanges are causing the volatility because the supply of coins on each of these platforms is extremely limited wen compared to the supply in circulation. This means that a small amount, like 5% of the total supply can easily crash the price or take it to the moon and we are seeing things like that happening every year.
IMO BTC can be a means of payment it only requires an economy built around it and people trading it directly, without having to use fiat.