I was contemplating the idea of getting a Standert when I was looking for a multi purpose gravel frame made of steel. But honestly, when you're looking for steel, the price gap between a (nicely made high quality) steel frame off the shelf and a custom made frame is not that big. As long as you're not buying from one of the uber-expensive boutique builders.
I went down the custom route. Got a nice fillet brazed frame and paired it with a Carbonda-fork. This is the result.
Wheels are custom built. Groupset is Ekar except for the Magura calipers and the Sram Red cranks. I'm using a 13sp chainring by Ratio components. Lovely ride.
Agree, in addition to the mentioned companies you will find regional builders such as Tannenwald, Big Forest Frameworks or Rennstahl here in Germany.
And if you are talking about steel, in Europe, you certainly must consider Italy. Cicli Barco or Legend by Bertoletti are just two I know and I am sure there are plenty more.
I am a fan and supporter of this forum, but classic steel imo is a different approach that makes me consider regional builders and custom options.