Years ago, before the small vs large blocks debate, I did the research myself to try and determine how large of blocks bitcoin would need to function as a global payment system.  My number was needing around 8 MB blocks for transactions of something like $10k+ to viable.  So, no, it is not *easy* to use solely the base bitcoin protocol and avoid off-chain transactions and 3rd parties.  You should have seen Anonymint's estimates for just how high transaction fees could go, they were astronomical.  Some of the estimates assumed miners colluding, but even the ones with no collusion were LOL insane.