Your interpretation is not wrong. "No tea no shade"/"No T no shade" is something that precedes what could be mistaken as gossipy/shady reads but is actually "real talk," just like you said-- brutal honesty. Some people started responding with "All tea all shade" as a way of saying "you lying bitch, you're not being honest." It was popularized into a meme thanks to a recent episode of Rupaul's Drag Race.
As for T/tea, when used alone, such as "What's the T/tea?" Again, it means what's the latest gossip, etc. And depending on context, it could mean "truth." I mean hello, we're talking about homos here, not grammarians. So nothing is set in stone.