I'm not sure how much I can add to this discussion since I'm such a "maintain the status quo" Crab (my opinion that nearly all the cards Crab got this cycle are **** and should not be trifled with could come across as elitist or dismissive), but I've found Flooded Waste to be sub-par in general.
The reasoning is as follows:
For the time being, there are two elements that typically fill the role of "stronghold province." Earth and water.
Earth because it has Ancestral Lands and Entrenched Position and Water almost exclusively for Rally to the Cause.
If you go through decks in the meta, I would say 90% of decks have one of those three provinces as their stronghold province. And the reasoning is pretty simple: You want your opponent to have to work a little harder to break the stronghold, so you need a bump in the road. Rally to the Cause is pretty much expected in a lot of cases (or at least suspected) when they don't run into a water province in the row, so good opponents will almost always probe your stronghold first. The reason Rally persists despite this counter play is because probing in itself is a very valuable delaying tactic. If your opponent has to waste a conflict just to pop your province effect, that may give you the opportunity you need to either break their stronghold (if you are neck and neck with them) or possibly impact their board with a water ring, fire ring or whatever to prevent the second attack from breaking (or at least force them to commit would be attackers to defend in order to prevent the ring effect). Or, if they're running low on honor, maybe an air ring will do them in before they can break your stronghold the following attack.
Not only that, but guaranteeing that at least one of your opponent's attacks is of the conflict type that you prefer is ideal. For example, I had a game at Gencon where me and my opponent were on each other's strongholds. He attacked military and I switched it to political (I saw he ran Fuschicho earlier in the game, so I suspected his RL card was Charge, though I hadn't seen him play it yet). I successfully defended and then attacked his stronghold political to break. He showed me his hand and he had all 3 charges in hand and he had a 5 coster a 4 coster and a 3 coster in his provinces. So Rally making his first attack political basically deactivated his entire turn.
And then AL and EP are obviously just for additional province strength.
I've found that Flooded Waste under stronghold is basically just a worse version of Rally to the Cause. First and foremost, 2 province strength is a lot. I often find myself successfully defending my stronghold by 1 or 2 strength, so dropping to 5 PS from 7 is a big deal. In addition, as in my example above, Flooded Waste would have just completely lost me that game, as he could have still played his charges.
I've also found that Flooded Waste in row is just as perilous. The first question becomes "what do I play under my stronghold?" If you choose EP or AL, then you're removing Defend the Wall from your deck, which is actually a pretty great province which has done a fair amount of work for me. So, if you run EP or AL, you're basically swapping DtW for Flooded Waste which...I mean, there are times when Flooded Waste can ruin a round, but there are just as many rounds where your opponent is just probing around and finds it and it bows a 1 cost character...
And the worst part about that is, you can't even choose to not defend that attack! Because, your opponent could just play a conflict character and break it anyway if they have a single boost (or the favor). Obviously, you're not too torn up about a 2 PS province breaking, but you'd like to get something out of the break, right? And bowing 1 attacker and then it still breaking because the PS is so low isn't really ideal.
The counter argument to that is you can play DtW and Flooded Waste in row at the same time. This means if they probe for Flooded Waste, they can run into DtW and give you a free ring trigger. Or if they're attacking heavy to avoid DtW, they could hit Flooded Waste. That sounds pretty good, but then what are you putting under your stronghold? I saw someone suggest Night Raid and...yea...I mean it's not horrifically terrible, but losing Meditations is a heavy cost and, again, probe attack on SH means they discard 1 card? Meditations is still a brutal province for your opponent to hit and is a very good Talisman target when SD is either destroyed or already initially attacked. The argument that your opponent is playing around Meditations all game is well received, but in open deck list formats (like the discord league and top cuts at Koteis), that's a non factor. So the unknown factor helps in swiss cuts at koteis and the pod stage of the discord league. Both scenarios, and again, this will sound elitist and I apologize for that, but you really shouldn't be relying on tricks to win in those sets of games, especially since those tricks won't work in the next phase of the tournament.
You could also just run a random "who cares" province under your stronghold like Manicured Garden or Meditations, but that's kind of conceding the point, in my opinion. If you're resigned to losing if they ever get to your stronghold, then you arguably aren't building a resilient deck, which isn't a very Crab thing to do.
At the end of the day, there are a number of variables that need to go "favorably" for you in order for Flooded Waste, as a stronghold or row province, to exceed Rally as a SH province, many of which are luck based (like they don't just happen to run into it with a weak character). I personally hated playing it. But your mileage may vary .