That is some circular logic with a built in invitation to tautology. Of course, if you accept the fact every non physical response is simply leniency, then of course it most be true that Biden is lenient. That is rubbish.
Your statement of: "Rule #1 is if you want to quell violence, the response must be immediate, significant, and even overwhelming" is an antiquated world view that is entirely not how the middle east reacts. At all. We have more than enough events to show that Islamic fascism never rests and never wearies and never forgets. Driven by the desire to rid the world of the Infidel, Islamic fascism is without any comparison in the world. Millions and millions were brainwashed by "the Great Satan". Millions and Millions were brainwashed by the occupation of Iraq, Afghanistan and the perceived unrelenting support of Israel. They will not capitulate, they will not stop and they never will. The British and French learned their lesson. We seemingly cannot learn from past mistakes.
This situation has nothing to do with appeasement and everything to do with (1) our physical presence in the middle east; and (2) our support and financing of Israel to the detriment of the Palestinians. Why not take the word of the intelligence sources of the world and in that region who say "you won't ever stop the Houthis and you won't stop the flow of arms from Iran into these rebel territories." The reality of Israel's response to Hamas is that there will be two more generations of Islamic fascists that are born from these events. I don't have any problems with Israel responding by they way, but at some point it must stop. See lesson 1: the fascists never forget and never forgive.
If you want to attack Iran fine, do so, but it won't stop the Houthis and it won't stop the flow of other arms. The destabilization of that region does nothing more than led to worse consequences. ISIS, etc. And then there will be worse consequences than ISIS. So ask yourself, given the nature of that region, what is that actually CAN be accomplished versus what you WANT to see accomplished.
If Biden struck at Iran 6 months ago, the right wing would have gone nuts--much in the same way a very sizeable portion of the right did when we actually responded with strikes two weeks or so ago. I would imagine that the same result would flow if Trump were president, and he did the same-the hard left would throw out the same babblespeak.
Social media is truly the bane of all existence. It amplifies everything to absurd levels of nonsense (like the throwing around the word "genocide" without a lick of understanding about what it means). The funny thing is, where was everyone when Milosevic was slaughtering hundreds of thousands of people? Nobody cared for 2 years.
I also find it insane that people only get their news from one source---the fox side or the CNN side. I do neither--I much prefer the Economist for a balanced approach that leads me read the facts and go for there.
Bottom line here: there is no such thing as appeasement. It is a word thrown around by mental midgets who simply deal in platitudes and politics.