I think the best answer is that SES are definitely more serious than ES, in that they depict a pretty horrible concentration of errors.
That seriousness stays, whatever error protection methods have been applied to the line - G.INP, interleaving, FEC, banding, high SNRM targets, or nothing at all.
As @b*cat says, a one-off isn't a worry. It is only when it becomes part of a pattern that you need to worry - and you need to take into account all the other things going on too.