That I homebrewed 5e so much(5e hardcore supplement), that it was better to just pick a different game like [D&D} Old School Essentials and add in a few things I liked from 5e.
I capped stats at 18, rolled all HD, passed on feats [optional], ditched stat bumps, rolled for attributes, used only the phb and it was still a cake walk for the pc's - got boring for everyone after a few sessions.
Me, I started 5e since Next, DM at GENCON '14 and local Adventure League for 8 years. As the glut of books came out, and the overbearing AL rules, people also became part of the problem.