My own experience of many years of earning and using BA Amex is very much at odds with thew OP's.

I've managed to use them for return journeys in CW and F for west coast USA, east USA and the far east. I'm sure many may not agree however I find a very good use of them is a short European break in in CE. I've never needed to have my hand hovering over the dial button at 11:55pm.

What I would say is you need to approach using them with a very different mindset than you would booking a holiday/flights using cash. Normally (after perhaps some research or a chat with the family) you'll decide on your destination and have a relatively tight window within which you want to travel. You'd then go about finding the best deal, flight times, accommodation etc that suit your requirements and budget and falls within the dates you're set upon travelling, which is usually a set two week window.

IMO with companion vouchers (and obviously reward bookings in general), you essentially need to go about it in the opposite direction. See what's available for the month(s)/season you wish to travel and then make YOU'RE planning fit around the flights and destinations available. Possibly have a country or continent in mind but that's about as restrictive you can be. If you've got your heart set on flights to Orlando with the outbound on the first weekend of the school summer holidays and the return on the weekend exactly two weeks later, you're going to be disappointed.

Think about heading, for example, to North America during July, August or Sept next summer. Or maybe Japan, Hong Kong or Singapore next spring. Then just see what's available when reward seats start to be released and take from there.

Apparently SEA, while not being the most difficult for availability, isn't exactly "wide open" either. Yet I've managed to get seats for 3 for next summer with relative ease. I was flexible with dates over a two month period and kept a close eye on seats being released. I didn't need to phone at midnight or book one way and then phone to have the returns added at T-355 days exactly. Once the outbound and returns were both available for the window I was looking at I booked online and it was all fairly straight forward.