As someone who was there at the time, OSI certainly didn't fail by being "overcomplicated". It failed because a) they charged money to read the standards documents and b) TCP/IP already had so much deployment momentum that nothing was going to supplant it (we see proof of this in the fact that IPv6 also didn't achieve that). Edit: also c) there was no requirement (unlike RFCs) to have an interoperable reference implementation available. So the implementations that were created mostly didn't interoperate.