I'd suggest Ramadan has little to nothing to do with this reduction in frequency.
As correctly pointed out already, why schedule the service to be daily and then reduce to five per week just a few weeks later? Its not as if Ramadan is a pop-up event which QR didn't know about a few weeks ago.
Secondly, the vast, vast majority of passengers using Qatar from CWL will be connecting onward to the likes of Australia, Thailand and so on. Very few will be terminating their journey in Doha.
Thus, the excuse of Ramadan is just that, an excuse.