adjusting its speed, removing its garrison, and reducing its cost or buffing its stats for cost, would go a long way to make this unit more viable.
Someone earlier pointed out that the resources get refunded. While this is true if you can keep it alive, the overall early investment in fuel can cut off many early options such as nades, bars/zooks, and even slow your overall tech.
The cost investment that is so easily killed can set USF tech back into the GG area as you have been so slow on tech you simply cant stay in the game
Brah, you can't account for a player's badness when designing a unit. Of course if you lose it it's bad. If you rush an AAHT and it hit's a teller mine it's also game ruining. That doesn't mean the AAHT needs a buff though.
Furthermore, "reducing cost increases early options". BRUHHHHH. First, bars and zooks early game? Are you ketten me? No one get's fast BARs (who techs bars to equip 1 squad early game) and zooks? Lel, that's the whole point of the WC51 - to counter the Kubel. You can still get nades, dude, it will just be delayed (as it should, since you have a garrisonable early vehicle). And again, you can refund the unit anyway, so one it comes out and does its damage and exhausts its usefulness, you refund it. If you are losing it, sorry, you're bad, no two ways around it, try Rifle company instead.
USF is strong anyway. It doesn't need the ability to field a WC51 and a M20 at the same time by reducing WC51 cost. Pick one or the other (or pick WC51, refit it, and get M20 anyway).
If you look at the grander scheme of things maybe you will see some other issues. Maybe the WC51 is thought of as being bad because it comes from a bad doctrine? Maybe it's bad because people are incapable of microing it correctly? Maybe it's bad because grenadiers are equipped with infinite range, target locking and movement seeking panzerfausts? In my opinion, the reason why it's not too good is because of the Panzerfaust from grenadiers. That doesn't mean the WC51 needs a buff though. It just makes it a niche unit. For example, consider it's usefulness against Kubel openings, Osttruppen openings, or MG42 spam openings. The WC51 could easily be used as a "free flank" tool against MG42 spammers, or be used to push Osttrupen out of cover in early game fights to nullify their buff.