Well with that logic, TD/AT taking out %50 of vehicles health with every hit is also bad design, specially against factions with garbage repair speed
Super heavy TD's are another issue yes (pak43 has natural hard counters, SHTD don't(map dependant (2vs2+mostly, pretty much unviable in 1vs1), but in most cases they don't). Higher repair speeds for soviets (which is the only faction facing this issue with tradeoff for high repair speed)wont help solving that issue.
Lower repair speeds for OKW though, will force that jagdtiger out of combat for a while if damaged, or force it to combat prematurely without full repairs, if under pressure. Which leads to risks and choice.
High repair speeds for everyone removes any risk and choice. Brainless. Which is the bad design here?