What's your incoming water temp? Raising 50 gal of water by 70F should take a 4500w heater element about
From what few samples I have of elec. WH replacement ages, only 1/4th get replaced this early.
I am always able to get hot water out of my tank drain faucet.
Perhaps you have a pipe or appliance somewhere mixing the hot and the cold. Finding that will be quite a challenge.
70 gal per person per day is about normal usage.