Now you, Dewayne, mention “all current scholars and grammarians, as well as teachers of Hebrew”—how many of them have read Tanakh completely through at least once? Or at the most two or three times? I expect that the answer would be zero. At least that’s my experience when asking professors. Oh, they know all the other major professors and the minutiae of what they have to say about the language, they have studied cognate languages such as Ugaritic, Akkadian, Arabic, modern Israeli Hebrew, etc. but how much do those studies help in understanding the quirks of Biblical Hebrew? Why wouldn’t those studies work against a person’s ability to get a working feel for Biblical Hebrew language?
Okay, let's get one thing out the way here: neither the Massoretes, Gesenius, or anybody else who studies or teaches BH is/was perfect. The fact that people and scholars are imperfect does not give us carte blanche to dismiss any contributions they may have made because they came to conclusions that differ from our own. Not to say our conclusions may not have value, but it's best to avoid the Lone Ranger mentality when it comes to language study. (And I happen to like the Lone Ranger character. Just an illustration.)
The value of cognate language study is that it often sheds light on rare Hebrew words that even the ancient versions (Samaritan Pentateuch, Greek versions, Latin versions, Syriac versions, etc.) seem to have not understood at all or misunderstood. At the very least, it is a resource that should be considered when translations and scholars disagree on what is meant by a rare Hebrew term or a hapax. They are from the same linguistic family, after all. In the same way, Latin and Greek often shed light on each other when considering difficulties in texts in these languages. The value of this study has been repeatedly demonstrated as in the cases of Akkadian and Ugaritic. Of course, any such study has its potential pitfalls, but that does not negate the potential rewards.
I haven't done any polls or surveys about the Tanakh reading habits of scholars, et al. However, from my own experience, I draw a different conclusion than you did about their competence. I took 4 Biblical Hebrew courses under a professor with a PhD. We studied the basic vocab and grammar first. Then, we did 3 reading courses. We looked at and translated and discussed passages from Genesis, 1-2 Samuel, Ruth, Psalms, and Jeremiah. In every case, the professor clearly was at home in the Hebrew text and had no difficulty whatsoever explaining it from the Hebrew prospective. At least in his case, I would wager (if I were a betting man, which I'm not) that he had read Tanakh in Hebrew numerous times long before teaching his Hebrew courses. Similarly, I can tell from comparing my own reading and the readings and grammar commented on by numerous Bible commentators and Hebrew scholars I've read that they too must have read Tanakh thoroughly in Hebrew many times.
My criticism of Gesenius is even stronger when it comes to his dictionaries. Not only were they derivative, not based on original research, but he was one of the founders of a school to teaching that was later named JEPD, then JEPDr, Form Kritik, or whatever nom du jour it has today, and his dictionaries were designed to push that teaching. BDB continued that tradition. The professor who taught the class where I first learned Hebrew, had us all buy Gesenius’ dictionary. The more I read Tanakh, the more I noticed Gesenius’ definitions don’t match the contexts. I bought Lisowski’s concordance in order to do original research, and noticed that Lisowski’s glosses tend to follow actual uses more closely than Gesenius.
Just because a work may have depended somewhat on earlier works in the same field does not necessarily make it valueless. All dictionaries, in all languages, have this defect, if you want to consider it as such. Your own dictionary came about eventually after your use of Lisowski. So, even if Lisowski did his work from scratch, your own dictionary is derivative. Does that make it worthless? I think not, not necessarily, as I have downloaded it and used it, along with the various updates.
I would caution against rejecting out of hand a linguistic work simply because you may disagree with some or all of the compiler/editor's theology or religious beliefs, or lack of such. The two do not necessarily bear on each other. To give a Hebrew example, Even-Shoshan's BH concordance is a valuable tool. I do not know his religious background, though it may be that he is an observant Jew. But whether he is or not has no bearing on the value of his work for learning Hebrew, unless it could be shown his beliefs have biased his handling of the Hebrew text. I am not aware of such if it exists. To use a couple of NT examples, William Barclay and A.T. Robertson both have produced useful works that illuminate the the Greek New Testament and the Koine dialect. They are pretty well polar opposites when it comes to their theological beliefs. I can look past disagreements with their theologies when they shed light on Greek. Once in a while they slip up and use faulty Greek arguments to support questionable theological conclusions, in my view. But their overall value is without question, in my opinion. You and I both regard the JEPD school as mistaken. However, that view of his does not necessarily devalue Gesenius' lexical and grammatical studies.
I expect, as has happened before, that you and I, Karl, will agree to disagree on Gesenius. And the Masoretes. And that's fine.