That is a bad trade for Houston and I'm pretty high on guys like Allen and LaVert, but that just isn't enough for a top 5 player in his prime. Even if Brooklyn threw in a bunch of 1st round picks it isn't good enough. You need a guy like Simmons coming back for Harden or it isn't worth doing. And Simmons might very well be available for Harden.
Generally when a team deals a superstar like Harden they want a young player back with legit All Star potential.
Aside from the draft, these are probably the 23 most promising players below the age of 25 (Giannis and Jokic are 25, but won't be traded anyway I assume):
Ja Morant
Tyler Herro
Trae Young
Shai Gilgeous-Alexander
De'Aaron Fox
Devin Booker
Donovan Mitchell
Jamal Murray
D'Angelo Russell
RJ Barrett
Luka Doncic
Brandon Ingram
Jayson Tatum
Ben Simmons
Jaylen Brown
Zion Williamson
Jaren Jackson Jr
Deandre Ayton
Bam Adebayo
John Collins
Domantas Sabonis
Karl-Anthony Towns
Kristaps Porzingis
Not a lot of them available for trade I think, since it wouldn't make much sense for the respective teams.
What do the bolded players represent?
Players on teams that have an experienced supporting cast to make a win-now-move by trading a young (potential) star.
Miami (Herro) has Dragic/Butler/Robinson/Crowder?/Adebayo/Olynyk
Sacramento (Fox) has Joseph/Hield/Bogdanovic?/Barnes/Bjelica/Holmes
Utah (Mitchell) has Conley/Ingles/Bogdanovic/O'Neal/Gobert
New York (Barrett) has Payton/Ellington?/Portis?/Gibson?/Robinson +/or cap space(?)
Philadelphia (Simmons) has Richardson/Harris/Horford/Embiid
Indiana (Sabonis) has Brogdon/Oladipo?/Holiday/Warren/Turner
I think for most teams that have a player on the quoted list above it doesn't make much sense to trade for Harden.
Either because the team is too young or inexperienced f.e. Atlanta/Memphis/Phoenix or since he's a bad fit with another player for instance Dallas (with Doncic while Porzingis is traded). Therefore I don't think that package by Brooklyn is terrible, since Houston will never get back equal value for James Harden.
To neutral NBA fans it would be a golden opportunity for the Celtics if they could trade for Harden by only giving up Smart/Brown + picks and finally getting that superstar to compete. But I'm unsure whether we should do that.