SR should not be considered as threshold value in any case, because players are not getting it doing individual things etc, but it is based on team win or lose(and you can stack winning team all the time, and with fresh guid you can get 7 SR in few hours). Using this value in any condition can cause that some players will never reach threshold value and will never be able to play any HW.
In my opinion Flo idea is much better, about checking how many times player was playing on our server, it will separate new joiners from regular players. Unfortunately there is no any reliable value which can be considered that player should be worthy to use HW.
I have another idea but I don’t know if this is achievable, we have this stats site with data like tdg etc, @Flo can we use the data from this statistics or it will to be slow?