The omission of traction control on the Triumph Speed T4 should not be a concern because, given the performance ceiling of the bike, you’ll rarely miss the system – if at all. The tyres, too, are commensurate with the Speed T4’s performance and should be a non-issue. If you do want better tyres, you have a wide variety of aftermarket options which won’t be very expensive either, so that should solve a potential issue for you.
The stalling issues on the Triumph Speed 400 are restricted to isolated units and aren’t very commonplace. If you buy a brand new bike that does have this problem, you should be able to get it fixed under warranty.
The KTM 250 Duke is a much more sporty machine than the two Triumphs and has some features they don’t, like a bidirectional quickshifter and a colour TFT display. It won’t feel as quick or as effortless to ride as the Triumph 400s because of its smaller 250cc engine, but if you enjoy revving a bike out to its limit and want to have that sort of experience, this might actually work in your favour.
Do bear in mind that the KTM will feel a little cramped if you are above 5’10”, and the Triumph 400s also have better suspension comfort. We’d recommend taking a thorough test ride of all three before you make a decision.