You can't compare S3/S3+ with the S5, S7 & S9. My S5 went up in flames after less than 5 months in operation. My S3 and S3+ are still in operation, they are built like tanks, not so with the S5, S7 & S9 which are based on string design, very weak design based on cost cutting measures not built for long term operation.
I have not had any trouble with any of them is why I compare. If you treat the miner good cleaning, proper power, etc. I still think S7/S9 will have a long life as a lot of S7's already have been hashing quite a while. S5 not a bad miner, and S5+ i loved as a miner it was honestly a great miner I was sad when I sold it due to my electricity cost.
But look at number of S7's out there still running there are a lot. So there are a few bad stories... but small number compared to total sold I would guess. Only one I ever had trouble with was a C1... and they were kinda a different best. It was really the water cooling company that was hard to work with not bitmain at least in my case.