I don't know that it's as simple as wingers getting less money than centres anymore. Lomax certainly isn't getting paid less money at the Eels than he was at the Dragons, and he's still playing on the wing there.
Wingers used to be treated as something of a joke - the fast blokes who got to hang around real football players. But the role of a winger has changed so much, and they are much more important to a team than they used to be. Look at someone like Brian To'o, who makes the yardage of a forward, is safe under the highball, and also an amazing finisher. Even Josh Addo-Carr in his heyday was a hugely influential player.
And centres are often used like an extra edge forward, which is why so many young players coming through get shuffled between centre and second row.
What was my point again? Oh, yeah - a good winger is probably worth more than an average centre these days. So maybe the stigma of being "just a winger" no longer holds.