The traditional view is to get the command experience first as this gives the best options for your further career. My observation of the careers of ex colleagues who went to the middle east big 3 is that those with previous command experience got (and passed) the upgrade much quicker than those that went direct from an FO position.
Not everyone finds the big 3 lifestyle a great long term option. If you have A320 command experience you have a lot of options elsewhere if things don’t work out and the time on the A320 may not delay substantially how long it takes to get a command on a widebody if everything does work out.