And what was the feedback from all the teams?
That they blistered from overheating. People are being insane about this, RBR and Ferrari put more heat into their tires, it's why they out qualified Mercedes anywhere heat into tires was an issue last year, Singapore, Mexico, etc. This also showed up in was it 2015 I think in Singapore and a couple other places.
Merc run cool tires, it's why they mostly go longer, Bahrain was a fluke and unintentional, a mix of strategies guys getting hit in pitstops ruining Vettel's second stop window. Merc were going easy to have tire life to defend from Vettel coming from behind on fast tires and took too long to push after a Vettel hanging out a one stop. Bottas's pace was slow, Hamilton gained an extra 7-8 seconds on that same stint catching Vettel then Bottas couldn't overtake and Vettel was going 3 seconds off the pace in the final few laps. Anyone can go that long and be slow, if the guy behind has poor pace and simply didn't push hard on his tires that's how you end up turning that into a win rather than losing places. Merc intended a one stop, Ferrari intended a two and got very lucky with race situation. Without the 5 place grid penalty Ham wins that race easily.
Merc run cooler tires, less good for qualifying, better for tire wear, Ferrari run hotter, way better for qualifying, less good for tire wear.
Yesterday the supersofts... the fixed to overheat less supersofts.... overheated so much on Ferrari and RBR that they couldn't do a full lap without them falling apart. But people think Mercedes cheated by getting them changed. If the original supersofts were used then what do people think would happen, Ferrari and RBR would have magically done much better laps on even worse overheating tires?
The slightly less overheating tires can't even last one lap in qualifying making them nearly useless, they'll be poor in the race, it was obviously entirely necessary as bringing a third tire type that is worthless for qualifying and the race would have been pointless.
Preseason tests are done, Pirelli get feedback and physically test all tires used. Merc didn't just spin up the tires, create blisters or lie about blisters as an excuse to beg Pirelli to change the tires a couple months later when they aren't dominating to gain an advantage. Pirelli decided based on all their information that a supersoft that overheats less is going to be a better choice for a few tracks where normal supersoft wouldn't cut it, where ultras and hards wouldn't make sense and they needed a third tire. That's the whole thing, it's got nothing to do with Merc trying to gain an advantage, this isn't a permanent thing, this is about Pirelli looking at how hot the tires ran in those conditions and comparing it to their data set for all tracks and saying at these three tracks we don't have a third choice of tire that fits the windows and a overheating less supersoft is the only alternative.