As you said, we have pretty good defenders already - I am talking about the Pels - Not the Hawks... You need a bit of both.... but you aren't going anywhere without top level offense in the current NBA... You can go pretty far without a top level defense - Pacers and Mavs were 24th and 18th respectively last year in DEF RTG - Both were top 7 in Offense PPG - Pacers were 28th in RPG and Mavs were 21st. Both teams eventually lost - but both made their respective CONF Finals. And the Mavs made the NBA Finals.... I lean way more toward OFF over DEF/REB in today's NBA... Especially during the regular season and pre trade dead line.
The clutch stuff is a mind frame, culture, and team DNA thing... Not sure how you fix that.