Yeah exactly. It correctly comes off as insincere when people say things like "you must feel upset". If anything that's the opposite of validation because the implication is that the speaker and any other rational human would not feel upset here but you must be so emotional that you need kid gloves.
Vs. actual validation which looks and feels more like an earnest attempt to understand where you're coming from
Interestingly (and I'm not sure if it was intentional or not), but the first thing kimbernator did here was validate your feelings.
"It definitely sucks when..."
Like ziddoap points out in another reply, the way it's said has a lot to do with whether it sounds patronizing and insincere.
If you speak like you're talking to a toddler "It sounds like you're feeling really angry," then yeah, they're going to hate it. Or therapy-speak like "You're angry for a valid reason" can equally sound condescending. But saying "that sucks, dude." accomplishes the same goal, in a way that sounds, and is, sincere.