well one thing is for certain is USF is in dire need of new hardware and toys to play with since axis is currently hogging and hoarding all of the best AT, armor and infantry in-game
To be honest that is a very poor argument for advocating a new unit, especially if it carries all the issues everyone just pointed out.
USF is lacking unit variety yes, but the problem is the core units' overreach in roles. What the Chaffee can do, means it replace not only Stuart and Sherman, but if it's penetration is good then also the M10. In the package of a Light Tank, no less. How can you justify high CP/ popcap and MP/F costs for a light tank that can perform so well?
The only other recourse is to make the Chaffee quite terrible in many other things...but then no one would even bother with Chaffee if it fails to do it' jobs well. Jobs that stock units already cover.
Bottom line is, whatever ideas that make the Chaffee a good idea, is inherently a bad idea because it automatically competes with Stuart/ Sherman. Which is not surprising: that was the point of developing the M24 in the first place.
If it's a doctrinal unlock it would have to be in like Captain tier, which means it still competes with Stuart...and also tempts the player to just spam Stuarts rather than get Major and Shermans. Given it's characteristics, you either get a very spammable light tank, or a hilariously unrealistic portrayal of a light tank that can do certain jobs very poorly despite realism.
Would be a nice unit for the mechanized company as it fits well in my opinion or for Recon Support Company instead of the Paratrooper Support Squad
If you've never heard of the Greyhound, that is.