Unless I'm mistaken, Dallas have one of the worst records in the NHL when it comes to drafting and developing dmen.
You're half right.
Drafting them, they are not bad at.
Developing them, you are 100% correct. They are very very hit or miss. Mostly miss.
Stephen Johns is almost lucky he had some time on the Hawks and the Hawks system otherwise he'd be another guy that they move out for nothing.
Nemeth went to the Avs and actually turned around his career a lot, he had a lot of promise, they sort of had him in and out, forced him to LD/RD, etc and then it didn't work so they called it a failure and moved on, he went to Colorado and completely turned his game around. So it's not even just us, it's more so just them not really doing well. Jyrki Jokipakka was another guy that had a lot of promise, his problem was that he went to Calgary, also bad with development, then he ended up in Ottawa and now in Europe.
Go back 5yrs for the Stars' draft record and if you look at even 2012-2014, it looks UGLY for how they draft and how little their "Texas Stars" do for development. The best part is when Nill was hired, he brought along what Stars fans thought was the success behind the Wings drafting, then it turns out their drafting just sucks even more with those guys there.