Delta's IT has hiccups...but TBH I'd say that the website is miles above the app (which can't process SDCs, among other issues). With that being said, I think the "looks nice trumps works well" problem is both definitely one Delta suffers from (I'm still annoyed at not being able to just slap in an airport code and go forward) and hardly unique to Delta (Amtrak adopted something similar in the last few years...though gee, I wonder where that came from?), particularly in terms of bungled mobile/desktop integrations (hence my occasional remarks about "Look at our new website, now with the reduced functionality of our mobile app!).
With virtually every company out there, I frequently want to scream "Look, get something working and then don't mess with it! I'll take butt ugly and functional over pretty and non-functional...
...but then again I would love nothing more than to be able to simply put in a few lines of code and be able to spit out pricing on any desired, legal or offered* itinerary without the "help" of a fancy GUI. Note that these issues are why I will also occasionally refer to website redesigns as a "jobs program for IT professionals".
*Not quite the same thing...DL will sometimes offer illegal itineraries for sale.