I'm not sure but i seems to see the opposite. When you check the slots payout of a RTG slot vs a MG slot, you can clearly see that RTG pays a hell of a lot much. I'll give you an example : Harveys vs Achilles.
Harveys - Achilles :
9 : None - 5/25/200
10 : 5/20/80 - 5/25/200
J : 8/25/100 - 5/30/250
Q : 10/30/100 - 5/30/250
K : 15/40/120 - 10/50/400
A : 20/50/150 - 10/50/400
Spec 1 : 20/60/200 - 2/30/200/800
Spec 2 : 25/75/200 - 3/100/500/1250
Spec 3 : 2/30/80/500 - 5/100/1000/5000
Spec 4 : 4/400/100/800 - None
Wild : 10/50/500/2000 - 2/25/500/2500/10000
Scatter : 2/5/20/100 - 3/30/500
Just look at the Wild section. On Harveys if you get 5 wild you get paid 2000x times your line bet, on Achilles you get paid 10000 times !
First special after the As, on Harvey's it only pays if you get 3 or more, 20x for 3, 60x for 4, 200x for 5, on Achilles it start paying at 2 for 2x, 30x for 3, 200x for 4 and 800x for 5.
From what i have noticed, MG slots pay less cause you hit 4 or 5 of the same often, while on RTG slots hitting 5 of the same is rare and if it happens it will pays VERY VERY good.