It’s not about easy or hard, you are feeling easy just because your real money is not on the line. The moment your real money is into the market, you are under emotions and loose trades. Demo is easy in that way if you are learning trading in your early years. It is easy because you get to have real market experience with no real money on the line.
You are right. Demo account will not teach you how to control emotion in trading. I recommend after demo account, invest small to learn about trading emotion.
Demo is never easy, if you are perfect in demo trading and can comfortably make profits, as long you are discipline, You will make it too in live.
I traded demo for complete 1 year consistently back in 2007 till 2008 when I got my first funding of over €200k, things changes from there and became proffesional trader having traded for various bank and private funds company.
Today I still trade on demo , but only when a client wants me to manage his/her live accounts on a broker I'm not familiar with, I simple open demo with that broker and run it copying from my live accounts to see how the broker speed performs.