I can understand your frustration.
I had a 2017 PD SR with DCT and must say I had a great run in the 2 years I had her (did around 66,000 kilometres before I traded her ) arguably the best car I've had out of 34.
Unfortunately, that doesn't help you. My SR was a tad hesitant in 1st gear when taking off (unless I selected sport mode) but that seems to be the way the SR dct was calibrated.
My wife's 2019 AWD Kona with a slightly detuned version of the same motor, had a much more responsive takeoff even in normal mode. Probably as quick as the SR in sport.
Never had the lumpy idle so can't help with that.. think a couple of other owners have mentioned a lumpy idle. I suspect an injector issue. The warm starting issue that affected some 2017/18 SR owners, was fixed with new injectors so there is a possibility yours was affected slight differently by the same components.