Standard Noise, as you rightly point out, it is important to keep a professional attitude to the guy on the other end at all times, if for no other reason, that if he is having a hard time, to add to his sense of pressure reduces safety.
Are you quite sure that your reminder to the pilot in your incident had not the least overtone of demanding to know what he was still doing there? I'm not trying to apportion blame - I'm just suggesting that it sounds as if there might have been a steady escalation of verbal tension on the RT that day...
You don't know what pressures we may be under at any particular given moment, just as we don't know what's going on in your world at that time. Important, therefore, I would suggest, to make a conscious effort to de-escalate any tension.
I agree with BOAC and 28L that the two phrases should be "Descend now FLnnn" or "Descend when ready FLnnn". Very little more RT and much clearer.