Wet steam

All steam gets very wet when it condenses, and that vent shouldn't let any (or very very little) steam out anyway (the vent is supposed to close when steam hits it). Any steam escaping from it is going to condense at or near the exit right where I see that drip in your photo.

That alone is not an indication of the presence of "wet steam" in your system.

I'm not a fan of that vent type, but it might work OK. Have you tried any other vents there like a Gorton or a Maid O Mist or Hoffman? (stay away from big box store vents, they suck)

What does "really cranks" mean to you? Do you know the high pressure limit of this boiler's pressure control? Residential steam boilers typically have just two modes that are visible to this vent: "Making steam" and "not making steam". There is no "really cranking" mode although pressure can build higher depending on the pressure limit control.

The reason I ask is that it may be that the pressure is too high for that vent to withstand, so it starts to leak steam which you see as drops of condensation. The pressure ideally should be like 1/4 psi or less

One more issue to ask a pro about if/when he comes by. Could be your radiator is tilted down towards the vent end so water has accumulated inside. It should be level or preferably very slightly angled towards the valve. You can use a couple quarters and an air wedge for this purpose if you're careful https://homedepot.com/p/Original-Patented-Winbag-Air-Wedge-and-Leveling-Tool-Lifts-up-to-300-lbs-WB20-SR5-4-40/303979798. Using a level, the bubble should just barely touch the line. We already know your near boiler piping is wrong and main venting inadequate and there's copper steam piping, and as @ethicalpaul suggested pressure may be too high. What's your pressuretrol set to? Why wet steam lowers efficiency: https://www2.tlv.com/steam-info/steam-theory/steam-basics/wet-steam-dry-steam. Varivalve has a high venting capacity, which is not necessarily what you want. Be sure to read this if you haven't already: https://heatinghelp.com/assets/documents/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-1.pdf

I had something similar in an old bathroom.  In my case the tapping for the vent seemed to be angled down a bit, enough it caused condensate to collect in the vent and similar behavior.  More angle than i was willing to try to fix by propping the radiator up.  My fix was a 1/8" street 90 into the tapping and then mounted a 1/8 straight vent on top of it. I think I added an extension too to raise the vent up an inch or so.  Did the trick with minimal fiddling.

OK thanks. A better descriptive phrase for that might be "a long call for heat".

So if it's only happening on long calls for heat, then it's when all the air has exited the radiator and steam is hitting your vent. You said above "steam was coming out of the air vent" which means the vent is just plain not doing its job (of closing when steam gets to it). It doesn't get much clearer than that as far as troubleshooting this.

Replace the vent with a better one is my advice. There's nothing wrong with the radiator.

I love The Heatimer company and Varivalves, but they  can be very finicky as you said AND if your steam IS too Wet, they will gush condensate like a Delta Faucet.  Mad Dog 🐕 

Me too.  Gorton or Hoffman.   Mad Dog 🐕