But how much was your vision score? I usually have 60 on Thresh and it's easy S if I have decent KDA with no more then 4 deaths and if I have good farm from about 30 minions. You should look to get one minion per two waves let's say. It won't give you much gold but it's for the S ofc and that way it looks innocently enough not to rage the adc. And wards. A lot of wards. With that it will be easy S every game. Usually that's the strategy for the S farming. You need to play to get the S. Stealing farm, getting kills (which shouldn't be a problem for Pyke) and having unnecessary desire to ward the whole map.
Your farm is good as I see for the duration of the game but the vision score is really important when playing support (and not only). 40 should be good I think but from begining to end I look to place wards. One tip: Place a control ward early on where it's hard for the enemy to take. Then after a while get another one (that's should be after 15-20 mins) and place it. You will get about 20 vision score from that. Then start placing control wards as normal until you reach the need of a last item.