Maybe they should've invested in a Center instead of dumping a huge amount into a pair of old RH goal-scoring wingers, when their best forward was already a RH goal scoring winger.
Trying to get Top-6 Centers is hard and expensive. Nobody wants to trade the ones they've got, 'cause if you've got a few of them, you've got realistic playoff ambitions.
The only things even close to consistent ways to get them are to either draft and develop them (which Nashville has historically been completely incapable of doing), or you have to go out and be willing to "overpay" by quite a bit to land outbid and land one who is too old/signed for too long in UFA. Where you're largely looking at guys with serious warts or major concerns about their age/health/footspeed/two way shortcomings/etc. If their previous team is willing to let them go, it's always going to be a major gamble.
But it still would've been better to gamble on something like that, rather than a winger/PP Specialist like Stamkos.