Okay,
@tetrasodium I tried to go back and weed through your response and grab the salient points.
Nine creatures
"assume a party of nine."
Not really sure why the party doubles it's average size or why it matters. I base encounters on the number of players.
Paint
"...blatantly adversarial...find some paint, & throw it over the dome"
This was under "prepared counters". Yes, I'm assuming some defenders may well have things in stock to counter things like the tiny hut. This isn't the first time it's ever been cast, I assume people know about spells like this and it's uses.
Particularly applies if the PCs are a known enemy and have used a tactic like this in the past.
Time
"...could have my NPCs setup an ambust and mercilessly TPK my players every time..."
I have no idea what you're trying to say here other than ... well never mind. I have no clue.
My point was that there is often a time constraint. You have to rescue the princess, stop the ritual and so on. In addition resting will give the enemy time to summon reinforcements.
Actions have consequences. I will never spring a deadly trap on PCs, but the enemy will respond in a logical fashion. They aren't just static piles of numbers that can only act if their zone is activated.
Burrowing and incorporeal
"Yes burrowing & incorporeal creatures can freely enter from underneath the dome as you suggest... Crawford actually said "There's no floor""
Yep, I acknowledge there was a tweet which I didn't know about it when I originally posted. I also ignore most of the sage advice tweets. I don't even always follow the official published sage advice rulings all the time.
On a related note, unlike wall of force there's no indication that the hut stops travel through the ethereal plane.
Portable cover
"... gets into all of the problems I pointed out in revised paint plus the TPK problem & taunt strategy of your Time solution..."
Again, I don't know what your point is. You seem to continuously envision some type of giant siege tower made of carefully crafted foot thick oaken timbers. I'm envisioning something hastily thrown together with scrap wood or timber.
It only takes a few inches of wood to stop an arrow. In the scenario in my campaign where this happened it was out in the open, there were torches affixed to the "wall" and hobgoblins with long bows hiding beyond the range of darkvision. So if a mage (presumably not the one that cast the spell) stepped out they would have been peppered with arrows. There wasn't a second mage so it didn't come up.
Also: since we're talking tweets by Crawford, he also stated that it was never the intent that you could make a ranged attack from inside the hut. Which, based on the wording (you can move an object in or out) is logical.
Block off escape
"...wall of force is a 5th level spell with only a 10 minute duration...the party of nine PCs..."
Actually I was assuming reinforced doors, cave-ins, brick-and-mortar. Again, you suddenly have a 9 person party for inexplicable reasons. Not that it makes much difference how many PCs there are, it's just an odd thing to repeatedly point out.
Run away
"...absurd solution that amounts to early in a session the gm simply saying annnnd the bad guys leave..."
Actions, or inactions have consequences in my game. If the goblins run off with the McGuffin, the group will have to chase after them.
Reinforcements/Ambushes/Traps
"... just expanding on the "Time" & "Portable Cover" solutions"
Again, so? The enemy now knows there are invaders. Why would they not fortify against them? Have you never seen the "prepare for attack" montage in movies? The bad guys have up to 8 hours of prep.
Poison gas
"Cloud kill is a 5th level spell..."
Why assume a spell? This was also under prepared defenses, I'm assuming containers of poisonous gas or similar.
Cage
"...as many as nine pairs of eyes able to see out from the safety of their unbreakable wall of force..."
Who says anyone is building the cage on the spot? This is a world with teleportation magic, giants and dragons. Yeah, it's a little cheesy and very situational. Also only appropriate as a prepared defense.
Flood the Room
"...Tuckers Koolds again... Good Jorb."
Very dependent on location and opponent. Like I pointed out in the post.
Put something hazardous on top
"Nine pairs of eyes and a dome ..."
Something hazardous could be anything from dropping a green slime on top to wasp nests. They'd need some way to block line of sight (fog cloud, darkness, etc) or maybe some kind of way to throw the material, perhaps an invisibility spell or two.
In a lot of cases it would probably be followed up in short order with a dispel magic.