I’m pretty much with Martyn Sinclair on this.
I can get decent BA deals if I book a long time in advance, and decent deals out of European cities (flying back into the UK and then out), and while I recognise BA’s biz product isn’t the best, it’s certainly ‘good’. Good enough for me not to want to spend an extra £500-1000 elsewhere.
When I can get a OW deal elsewhere, I’ll take it – Finnair to China, for example (going next month). Finnair has a great business product and its fares are very reasonable. Flying Finnair to China via Helsinki is way cheaper than flying direct with BA, and you get more TPs as well.
The Avios and TPs carry weight as well – it would take me a long time to build up the equivalent elsewhere.