You can't get both upgrades at the same time? That's dumbtarded, yoYes you can, so far anyways.
You just need to select the other upgrade before the first one is finished, otherwise the option would disappear. So if you got 110 munitions, you upgrade panzerschreck and wait for munitions to get to 30, then select minesweeper. If you time it right, the game won't lock out minesweepers.
Yes, it does require you to commit more munitions into a single unit in a timeframe, but the end result is a Sturmpionier squad with both upgrades.
IMO I think it's okay, you're just concentrating more munitions into a unit that is either going out attacking tanks, or staying put to repair stuff; either way, you've committed munitions for mutually exclusive roles: you can't repair stuff, take on infantry and take on tanks all at once. And even if you could, you're making them perform three roles where other units can manage two of them. That's considerable risk in munitions investment and tactics just to have a unit fill more roles. The only real problem is that, of the three roles Sturmpioniers can fill, their initial role of StG44s can be replaced by another unit.
And if you're holding back munitions for the dual upgrade, you're also holding back 120 munitions per squad from other things like panzerfaust/ StG44 upgrades.
And of course if you're short on munitions, you're forced to choose one or the other and be forced to spam Sturmpioners to fill a greater role.
In that regard being able to get both is fine to me, they already cost munitions on a unit that can't to all of them at once and itself is expensive. It's either that or Sturmspam.