Can't say anything about ease of money making but can surely add my two cents on "writing or buying".
Every time an option is written a fresh contract gets added so OI has to go up.
An option may be bought from a writer (OI going up) or from an earlier buyer (OI remains same) or it can be bought back by the writer (OI going down as the contract is extinguished).
So it is safe to say that if OI is going up - it is writing and if OI is going down it is buying. I am afraid that money making still remains difficult.
regards.
rm