Those barbs are notorious for breaking. So much so that Dorman created a solution.I'm sure that will hold for a while, but like I said,... that barb comes free with a new radiator. lol. the material is glass reinforced thermo plastic, epoxy does not really adhere to it.
The solution you have will hold until it doesn't, but longer term (assuming you don't want to fork out the $$ for a new radiator for now) if/when that fails, use the Dorman.