Mozart
There was and is no reason for concern about De Kock's form. He was a key player in the 2020 IPL - but also stared badly in his first two matches that year and ended up scoring over 500 runs ending up with figures better than Du Plessis and AB combined in the 2020 series.
In the IPL series this year he started off badly as the case was last year abnd ibn the enxt three matches, In the next three he helped Mumbai Indians to win in twi games and pklayed a significant role in winning the third match.
I think the main reason for the questionable form of De Kock was the effects of the total demoralization of the Proteas over the last year through defective selections ands coaching while he had to take the blame for the continuous losses that followed, The fact is that he was not the only one that was demoralized by the faulty selection issue - Rabada was another problem case in the now suspended IPL this year.
As to Du Plessis he started off like a house on fire the in the IPL last year and was a total flop later in the season He came back to SA and was a failure playing for the Proteas and them announced his retirement from test cricket and apparently ODI's as well. He wants to play om the T20I WC this year - but could potentially be the same failure as was the case of Amla in the 2019 ODI World Cup.
There are younger and better players than him who are playing provincial cricket in SA - but he has the support of the idiots who claim that present Proteas own their positions in the team can cannot be replaced irrespective how poorly they perform for the Proteas.
The essential need for the Proteas is to start rebuilding the team and start with players younger than 28 with a real chance for development and not the way it is done at present,