Luckily South Africa are utterly garbage outwith their 3 gun players.
I see your point, but I'm not sure I agree.
After Steyn, Morkel and Philander have done well at Test level. Philander seems to be getting back into form and bowled well in the first Test against India. After those three the back up seamers are Rabada, Abbott, and De Lange (probably in that order) who are all better than the Poms' back ups.
Our top six isn't looking too bad either - AB is AB, Hash will find form sometime, and Faf has been unlucky so far in the Tests India - he was batting well in the ODI series. Our openers are maybe slightly more iffy but Van Zyl and Elgar haven't done anything to make me doubt them yet. Our number six is probably the most vulnerable spot - Duminy hasn't really kicked on in his career, and I still have my doubts about Bavuma.
With the keeper, I'm not sure Vilas will play against England - De Kock has been keeping well in SA, and is in good form with the bat again, so he'll probably come back for the Tests (unless Vilas does something amazing in the next two India Tests).
And probably for the first time ever after isolation we're close to equal in the spin department. Ali is probably better than Piedt, Harmer, and Tahir, but not by much, and all three the SA spinners are better spinners than Patel (although Patel does offer you something with the bat).
That said, you have made me reassess what I said - England probably won't get hammered, but SA still looks like they'll take the series.
Anyway, SA and England always produce awesome Test series and this one won't be any different I don't think.