Indeed. While it is not my favourite kind of football, until FIFA/UEFA/FA do something about the diving and failure to try and stay up, players will continue to do this and you can either not do it and have a disadvantage over teams that do, or you just play the game according to the de facto rules in place at the moment.
If the powers stop this shit about not being able to do things afterwards if the ref has already dealt with the situation and apply retrospective yellows, reds and suspensions (not fines which are a waste of time) then this and other offences will continue. (This is if Theo was considered to have dived when not being fouled). They do not seem able to understand that correcting decisions in the cold light after a match when video from many angles can be studied - something the ref cannot do at the time - does NOT undermine the refs authority. Refs will still have to continue to do their best with what they perceive at the time. An odd mistake is to be expected and is nothing to be ashamed of. Pretending mistakes have not happened, however, is something they should be ashamed of.
So while Theo might have been able to stay up, he was correctly playing the game according to the current interpretation/application of the rules. Wheater knows full well that if he pulls back a player in that circumstance, the player is likely to go down - the ref might see it anyway - and he is going to get sent off. The fact is, Theo was fouled by his shirt being grabbed, so whether he went down or not, Wheater committed a dismissable offence. End of story.