It's difficult to draw any conclusions from two tests; any weaknesses were already apparent. This habit of following impressive wins with limp performances was a habit during Cook's reign and Root will need time to change the team's mentality.
They were excellent in the first test but a lot of it was down to the performances of Root and Moeen (I've often been critical of Moeen but he can pull out great performances now and again).
One big thing that is still obviously an issue is the batting: I think that England's one-day improvements have had a detrimental effect on the test team, and they need to find a proper balance (not a Ballance, though) between positive strokemaking and grinding out big scores.
The senior players - Cook, Root and Bairstow - are not doing enough to support the rest, in that they are not making big runs themselves. They have healthy averages but
as I showed a few pages back, they're not playing the innings that really matter. Root got a big score in the first test but again here he failed to turn a flashy 70-odd into something that really put England into the match.
Bairstow has now passed 40 fourteen times since he last made a century. Eleven of those times, he has got out before reaching 60. There is something very wrong with his concentration.
If Ballance is to go they need to do it soon so that the new man - Stoneman or Westley? - can get some experience against the SA attack, rather than coming in for the easier ride that the Windies will provide. Jennings looks very shaky. One hopes that Hameed can rediscover some form.
The bowling is a worry, as well: who will replace Anderson (and indeed Broad) when the time comes? Wood has not impressed and Woakes will presumably slot back in for him, Finn's time has passed, Ball hasn't convinced... this guy at Yorkshire has been getting wickets.
I am not sure what Liam Dawson is doing in the team. Surely they can find a better use for that position.
South Africa are also a team in transition following de Villiers and Steyn's retirements. They have a similar mix to England, of established class acts (Amla, Du Plessis, Philander, Morkel), exciting youngsters (de Kock, Rabada) and guys who don't seem to be up to it (Kuhn, Bavuma). Two well-matched teams with lots of strengths and weaknesses: makes for an unpredictable and thus far absorbing series.