Given that teams knew we had money, he was on a long contract and they had paid £6million for him 6 months earlier then it's not an unreasonable fee.
Also when you contrast his impact compared to Ramirez who cost the same amount...it's a good analogy that. Long is worth that amount because of how positively he affects the team and fits into the system. Ramirez is undoubtedly the technically better player, but is he worth more to us than Long? Absolutely not.