Since you seem to be blissfully unaware, USF could do nothing but spam rifles for 4 years, that changed only recently with their tech rework, allowing them to actually use any other infantry then rifles in higher quantity then one without hogging most of your pop cap.
There isn't anything wrong with rifles and they most certainly do not need to be incentivised more then they already are.
They are perfectly fine and strong squad.
I am completely aware of how things used to be.
There have been many things that contributed to the original problem none of which involved the price of Riflemen.
The original problem was primarily due to Riflemen being too good at everything with smoke, frags, BARs, AT riflegrenades, and Bazookas plus getting free veterancy with rifle company. Yeah. They were a bit much, and that’s an understatement. But they are now heavily sidelined by losing a lot of this utility while other units gained either power or utility in turn. A cost reduction from 280/28 to 270/27 is an incredibly minor change that won’t really do anything except make using Riflemen as your mainline troops less punishing on manpower, especially late game.
That’s the whole point of the bigger infantry squad upgrade on all mainline infantry squads. It’s not supposed to make them better than specialist or elite squads, just more economical.
Long story short, I think a veteran sergeant squad leader upgrade for Riflemen is viable and potentially balanced if done right. Riflemen are not OP or UP at the moment but could use an ever so slight reduction in cost to reflect their intended role as mainline troops and reflect their reduction in utility compared to what they used to be.