But, when bitcoin does become more adopted and popular, we are 100 percent going to see more transactions, which means higher transaction costs and slower transaction confirmation - which can be easily countered, if we get more miners in the coming years where bitcoin makes it big.
More miners will not sort the slower transaction problem 
, we are improving with time and Lightening network is one solution that can be implemented to over come those but you cannot expect everyone to follow that, even if we have less miners we can adjust the difficulty level and carry on the process, if you get more transaction per day your transaction gets stuck and the users paying the higher fees will have the priority and this is a capitalist theory bitcoin is following 
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