I'd definitely not waste the miles on this. By the sound of it, you're looking at Flex rewards, which are a big waste of miles. For 80,000 miles each, you could be redeeming a J saver.

For a lower fare on LHR-DXB, book onwards to the Sub Continent or somewhere else. Fares to DXB are always higher, and you should get a better deal that way.

Saver seats are available if you are flexible with travel dates. Sometimes they only open up close to the date of departure, and on some routes they are really hard to get (like LHR or JFK), but they do exist. If you can make plans well in advance, this should be a lot easier.

Hope that helps, and welcome to FT.