Referring to the quote in the OP, I don't see how FGW is unique other than being the only "inter city" TOC still using diesel power.
It is unique due to the diversity of its operations. It has long distance daytime inter-city services, it has an overnight sleeper operation, it runs a massive London commuter service at the same time as it runs services on very rural branch lines in the South West and inter-regional services from the South Coast to Wales. There are very few TOCs (if any) who run that broad a spectrum of service types.