As supporting casts? No, they aren't that good.
They do nothing to fill in the a team with Lebron on it.
A Lebron led team needs defensive players, and neither of them are it. It's like putting Kobe next to Mike in his prime, it's not really a good support for Mike, because he duplicates a lot of what Mike does, and does it worse. Or how Kevin Johnson was traded away because the Cavs had Mark Price.
Irving offensive skill set overlaps a lot of what Lebron does, and does it worse. Irving doesn't have the same abilities to involve teammates, he tends to hold on to the ball too long, and is primarily an ISO oriented player. Lebron could be that, and is much better than him at it.
Love rebounds well, but he is just a bad defender. He seems to have trouble grasping defensive concepts (I don't think it's a lack of effort).
If either of them can reinvent themselves and fill in a role, then great. If not, they are not great supporting casts, at least not specifically for Lebron.