And there would be some who would howl at you if you put it like this. And it is a question which is much less loaded than that of the men's versus the women's tour. I feel this should explain the controversy around it that you find dumbfounding.
Well, there are plenty of women stronger than me, I can tell you that.

But of course that's not the point. I certainly agree that tennis is quite a physical sport. On average as well as at the extreme top end, which we are talking about, men do outperform women in physical terms. While tennis is about more than pure physicality, there is no reason to expect that this does not have a serious effect in tennis.
(There
could theoretically be other factors that come into play. For example, in snooker I tend to believe that it is social factors - the male-dominated culture of clubs - that contribute much more to the gap between male and female players. However, I see no evidence that such factors should impact on tennis, or at least, in a way that would negate the above-mentioned physical differences.)
So yes, it is a reasonable proposition that top players in the women's game would be unlikely to be able to compete at the highest level on the men's tour. It is when you are taking a
specific top women's player, and start bandying around
specific numbers (700 in this case) that you are stirring controversy.
Now, I have no good basis on which to form an opinion on whether Serena would have trouble competing at a similar level to ATP World #611 Wishaya Trongcharoenchaikul, but at least I don't find it as obvious as you apparently do that she could not.
Now, there are some reasonable objective numbers that it is possible to consider, such as serve speed, speed of groundstrokes, running speed etc. These do not tell the whole story, but if you could show that ATP World #611 Wishaya Trongcharoenchaikul consistently outperformed Serena Williams on such metrics (enough to outweigh any other advantages that Serena may have, such as tactical finesse, versatility and mental strength), then that could lend some weight to your argument. However, I doubt that either John McEnroe or you have really done an in-depth analysis of the physical capabilities of someone such as ATP World #611 Wishaya Trongcharoenchaikul, weighed against those of Serena Williams.
Hence, the controversy.