There has been a +20% attack stat and +20% defense stat buff for all defenders for at least 18 months. @SolemnWolf and @RedPython worked out its existence when figuring out the damage equation last year, I believe. It has almost certainly been in place longer, but I don’t know how long.
DOTs increase with troops +attack, and with that 20% attack buff, but not with temporary buffs like BT.