I like TLC, personally, but yeah it's way weaker compared to ToD and RotLA. For me I only hate Skull at this point and won't watch it. Even it's figures kind of blow.
Comic relief in Indy should be somewhat limited. Indy and his dad was plenty sufficient in TLC but they took it a step too far by dumbing down two secondary characters for no reason.
I attribute that to Spielberg's deciding Temple of Doom was too girm and his comments of how he horrible he felt by depicting child slavery (Villains can't hurt kids?). So instead he goes on and trivializes Nazis by making them fantasy movie villains...again. (He made up for it with Schindler's List later).
Self-parody for a franchise that was already part homage/part satire of a genre is a bad idea. Spielberg said "I had Indy's dad played by JAMES BOND." Yet, he didn't quite learn where the Bond franchise started to falter...self-parody.