This very good!
OK, so your "1 year ROI" calculation is more like "number of bitcoins mined in a year" given different average difficulty increases every 2 weeks (and your sheet 2 shows historical data for the difficulty increases).
I think "number of bitcoins mined in a year" would be a better name for this calculation.
You then need to subtract the yearly electricity cost and the original cost of the miner from the "number of bitcoins mined in a year" to get the "Profit" which will often be less than zero (i.e. a loss)

The ROI will then be "Profit" / "original cost of the miner" and will be a percentage.