Feels like cope when you could say that at almost every by-election, I would imagine increasing your total number of votes at a by-election is a pretty good result regardless.
I might be wrong but I think they are both record breakers or near to in terms of swing. Tamworth is apparently the Tories 55th safest seat.
I think a better justification is that it is hard to have two worse departing MPs so you can understand the disillusion felt by voters in those parts. Pincher was a very high profile scandal and made not only himself but the government look like complete shit. Dorries has a negative IQ and seems to have got into politics to help herself and nobody else.