In some ways, I agree with you on principle but is this pragmatic in reality? In January, we supposedly spent 4 million on loan fees for Ighalo. He has scored 5 goals for us. We will have him 18 months and get nothing back for him. £4m spend = 5 goals (I doubt he'll get many more).
I dare say Haaland would've done significantly better for us and given a big boost in terms of results, the excitement of having a new global star and so on. If we'd have signed him at 17m and sold him at his release clause of 63m (supposedly), yes it'd be a kick in the teeth but, aside from our pride, that's a 46m profit on a striker that would've likely scored far more goals than the 5 goals Ighalo has scored for us for a 4m loss.
I would also assume we would pay lower wages for Haaland than what we pay for Ighalo's inflated Chinese team wages. Maybe I'm wrong there. Also, there's a chance Haaland would've loved it so much here he'd sign a new deal without the release clause.
Educate me, someone, because maybe I'm missing the obvious but what would be so wrong with this? I know I'd rather have signed Haaland all day long. Better to have loved and lost, and all that.