Inactive for years due to patches, because the methods on how to counter it are unchanged since day 1 it was introduced.
Stuka for OKW, FHT or pair or mortars for ost.
Alternatively, engage, make them pop buff, retreat for 30 secs, engage again and stomp.
If all forces are concentrated there, cap empty map.
The methods on how to counter it? You mean like flamethrowers or fire in general? Don't get me wrong, it used to be stupid easy to set buildings on fire with a flamethrower but now its a real pain in the butt.
In case you've forgotten, it was ALWAYS annoying to fight against, but the commander it was in was absolute trash. Now that urban defense has been buffed,its a meta commander that is actually viable, so we see FHQs a lot more-and the issues with them have become more obvious.
FHT is the best option you listed primarily because it will fit somewhat organically into an ostheer build. Just like double flamer pios would have been a counter once upon a time.
Double mortars will completely throw off your build order as ostheer.
Stuka is a counter sure, but that's only if you opted for mechanized, and you are investing far far more resources into the counter then the cost of what you are actually countering.