Green’s Dictionary of Slang

important, influential.

1972		E. Grogan Ringolevio 140: Othello was [...] a heavyweight put-on artist.
1981		J. Ellroy Brown’s Requiem 171: A long time ago he got away with a heavyweight scene.
1999		Guardian Guide 29 May–4 June 75: A housemaid is found dead in a hotel bathroom during a function for heavyweight local worthy Felix Wilson.
2000		J. Hawes Dead Long Enough 9: If a TV Exec is going to put himself and his balls on the line for anything, it will be for something that combines proven ratings and alleged heavyweight learning.