You're right about the Stealth disadvantage removal, it's applying in general instead of to just medium armor. But it doesn't apply +3 DEX to heavy armor; DEX doesn't get added to heavy armor at all, in practice. If you're seeing that happen, make sure you're not wearing medium armor and heavy armor at the same time, since if you have better quality medium armor with +3 DEX (like scale mail, 14 + 3 = 17 AC) it could outdo basic chain mail heavy armor (16 AC).
The title feat seems to removes the stealth disadvantage for heavy armor as well as for medium, and I believe it also allows the +3 Dex bonus as well.
You're right about the Stealth disadvantage removal, it's applying in general instead of to just medium armor. But it doesn't apply +3 DEX to heavy armor; DEX doesn't get added to heavy armor at all, in practice. If you're seeing that happen, make sure you're not wearing medium armor and heavy armor at the same time, since if you have better quality medium armor with +3 DEX (like scale mail, 14 + 3 = 17 AC) it could outdo basic chain mail heavy armor (16 AC).
Helpful rewriter of Japanese->English translation and delver into software codebases (she/e/they)
This Stealth disadvantage removal on heavy armor issue has been passed along!
I probably did have both on at the same time... just compared half-plate w/dex to plate, and came out good