English speakers are perfectly capable of pronouncing ch vs sh (e.g. chair vs share) whereas sh vs sh’ (ш/щ) might be more challenging.
Especially since there exist words in russian language that actually have "т" before "ч", and the sound it makes is different. Compare "отчёт" and "очки" (the closest similar word i could think of by the sound of the first half of it). If you try pronouncing the first word as if "т" wasn't there (or the second word, but as it "т" was there), it will sound both very different and wrong.
/t͡ʃɛə(ɹ)/
I think it makes sense. To me there is a clear difference between chair and sheet, where chair starts with the sound of a t. Same thing with Ч.
Everybody expect the French won't have any problem reading out without stumbling Chkalov or Chmil. Supplying the /t/ is a copout to please the French and, as a bonus, to piss of the Russians (especially the Chekalovs ones).