I think you should be careful about generalising.
My impression of the book is that it was mostly based on his own, first-hand experience -- "I saw and heard a monk say such-and-such".
If it is first-hand experience, and his experience as a monk, then how can it be called "poorly researched"?
It reminds me of suttas, which begin, "Thus I heard."
But generalisations are difficult. Consider for example the first sentence which ruben2020 quotes above, "Buddhism has today become overgrown with a mass of superstitions". I can easily imagine someone resisting that conclusion, and replying, "That's not true! The Vinaya is unchanged..." and so on.
Incidentally I searched the two texts you cited for the words "baseless" and "misleading" and didn't find them. The word "researched" appears in the first:
At less than 80 pages, it is somewhere between long essay and short book, and is at turns angry, funny, cutting, astounding, and, unfortunately, sometimes poorly researched.
You ask, "is it poorly researched" when the exact quote is, "sometimes poorly researched" -- I think that's a big difference, i.e. the first ("it is poorly researched") implies that the whole of it is "baseless", and the second ("it is poorly sometimes researched") implies that more could be added on certain topics.
In summary it seems to me that Ven. Dhammika made some personal observations -- and from these he generalized somewhat -- and I'm not sure why, perhaps he was wondering whether other monks might make similar conclusions, have any similar "views".
Your quote ends with,
For some, Bhante Dhammika’s casual relationship with facts and tendency toward generalization may limit their ability to take the thrust of his arguments seriously.
... and I think that's what I'm saying, i.e. that it's the "generalization" if any that makes it questionable, or perhaps not easily "actionable" or something like that.
Incidentally I think that American law -- I don't know if you're interested, but I am because law tries to define which might be difficult to define -- distinguishes between "opinion" and "false statement of fact". For example if someone said, "I think you're an idiot" then that's an opinion, and if someone said "I saw you stealing" then that's a statement of fact (which may be true or false). I'm not aware of Ven. Dhammika's making any false statement of fact; it's possible you may disagree with some of his opinions. It's been years since I read it but from what I remember he narrates (or "is transparent about") experiences on which he based or from which he formed his opinions.
I admit that some sceptics might prefer data based on more than only one person's experience.
I found what he wrote interesting -- whether or not I share ("agree with") his opinion, I liked being able to share some of his experience -- to "see though his eyes".
As for "angry" I don't remember that. Perhaps that means it evoked no anger in me: that I didn't read it as angry. I read it more as "disappointed" sometimes, perhaps "sad", "disillusioned" even -- and worried, that the Vinaya isn't being practiced properly and so people don't benefit as they otherwise might. I also saw it as looking for leadership and/or suggesting direction -- "This is right, that is wrong, we should not behave like that".
Incidentally I think that part of the genius of the suttas is their making generalisation which are true -- which isn't easy, and may be a science. Usually though when someone makes a generalisation you might be able to say, "That isn't always true" But maybe personal experiences are "true", "This is what I saw", and leave people better informed, i.e. with a more complete, more factual, more detailed picture for what that's worth.