You would be suprised. Most tanks with good pen at Rank 1 actually have practically no armor and can be killed by a round that can penetrate 20mm.
I’m not sure whether the 47mm APHE is really a downgrade when it can kill a lot more vehicles in one shot. If you need more pen you have a 75mm.
Currently the only downside is that the 47mm APHE gun reloads in 6s compared the solid shot 47mm launcher that reloads in 4s but that might be adressed in the future.