Benignuman:
I don’t see why Tosafos should ask his question in reverse. The answer about davening is a bigger ukimta than the answer about zivug sheini. There are two ways to learn the stirah in sotah. 1)Rav Yehuda Amar Shmuel’ statement is in stirah to Reish Lakish’s statement 2)Rav Yehuda Amar Shmuel’s statement is in stirah to Rabba Amar R’ Yochanan’s statement. (Rashi explains it the first way, but see the Maharsha who points out that in Sanhedrin the Gemara explicitly asks it the second way.) Now using the answer of davening would mean that Reish Lakish or Rabba Amar R’ Yochanan’s statement is only applicable in a case where a person changed his mazal through tefillah (which incidentally we would have no way of ever knowing if this happened). Whereas the answer of zivug sheini is just that they were discussing second marriages. It’s only according to your pshat that the answer of davening would be advantageous to use in Sotah. The only advantage that I see in your pshat is that you can answer the Maharatz Chayes’s question. But I would allege that the Maharatz Chayes was forced into his question because he read the lashon like me i.e. that Shmuel’s din only applies by a second marriage.
As for your point about Reish Lakish, I hear it somewhat, however according to the Maharsha’s understanding the ukimta would only be in Rabba Amar R’ Yochanan’s statement* but not in Reish Lakish’s statement. According to Rashi’s understanding the ukimta is in fact in Reish Lakish’s statement, in which case Reish Lakish was saying that only second marriages are lefi ma’asav. But I don’t think that means that you can only have a sotah from a second marriage. It’s just as possible if not more so to have a bad wife in your first marriage (as I explained in my last post). The only thing is that you’ll ask what Reish Lakish’s statement has to do with the parsha of Sotah. Good point. But I could suggest that perhaps Reish Lakish was pointing out that in a second marriage you would only have a sotah if the man was bad. I admit it’s not the best answer.
*Perhaps you can argue that the Maharsha agrees that the way Rashi explains the Gemara’s question is in fact a valid question for the Gemara to ask and his only point is that there was no need for Rashi to explain the question that way when he could have just explained it the way it is clearly meant in Sanhedrin.
P.S. You are welcome. It brightened up my day too.