Im not sure we would have to offer more than Brown. Who else is offering a better player? Miami giving up Herro?
Two divisional rivals are offering better players in Toronto offering Siakam and Philadelphia offering Simmons
This is speculation of course, reasonable speculation, but it is not known for example that Simmons has been actually offered. I do agree though in that if Brown + Pu Pu Platter of contracts was the best offer actually on the table for Harden, I would wait if I was Houston. There is no need to rush to get this done. The offers will likely get better until the trade deadline.
Simmons is the plum in this but do they (Houston) really want to make a deal with Morey? And as to Siakam, I am not sure he is all that much more valuable than Brown. I am not that big on Siakam. I have them fairly equal, in the same range, but I give Brown more ceiling. As with a trade based on Brown, I think Houston waits if the best offer is Siakam and whatever additional contracts are needed.
The rumor is that Toronto and Boston are the favorites. I find this plausible. Miami is out, Philly may be out because Houston does not want to help Morey. That leaves Toronto (Siakam) and Boston (Brown). I bet Brown + Smart gets it done but not just Brown and contract ballast. Not sure good young player(s) Toronto has to add to Siakam