| As a 20-year trial lawyer, advocacy professor and college public speaking instructor, I have thought about this topic many times. It is a sore point for me. I have taken over 200 hours of courses/training in teaching methodologies, advocacy skills, public speaking, etc. over the years, and taught about 75 law school, undergrad and college courses, about half of which are directly on topic.
In the Stake I lived in, I did an annual seminar for three years on how to give better talks and lessons. It was remarkable how little people new about basic public speaking and communication principles, let alone developing actual presentation skills.
Over the years, I also consciously analyzed talk content and watched Mormon congregations as they listened to talks. From a TBM standpoint, I would say about ten to twenty-five percent of church lessons and talks are solid. If you are lucky, on average, you will hear an "excellent" talk, lesson, fireside, etc. about once or twice a month. The exception would be where there is an "excellent" Gospel Doctrine teacher or perhaps a vibrant humanistic leader in a ward. (These are few and far between IMO.) Overall, about 75% of your listening time, as a BELIEVING Mormon, will be completely wasted. (The same percentage applies to Mormon books, lesson manuals, etc.) Mormons could argue that principles like repetition, simplicity, reinforcement, democracy of participants, etc. make that number lower. While those principles may be valuable to some degree, I don't buy that they outweigh wasting hours of people's time with frothy, poorly-prepared, repetitious, mind-numbing or brainwashing content.
To answer your question, Mormons are never taught the required skills in any formal way. All of the Mormon skill acquired comes from experience. IMO, due to extensive opportunities (church speaking, lessons, missions, callings, etc.), the average Mormon ends up substantially ahead of the average non-Mormon in terms of public speaking skills and abilities.
Unfortunately, IMO, that advantage is far more than negated by:
(1) the complete lack of any structured training in public speaking and presentation skills (other than perhaps the "sales techniques" people learn in the MTC);
(2) the "straightjacket" restriction on the content permissible in Mormon settings and the corresponding assumption that the content will be based on the Mormon checklist of required beliefs and assumptions;
(3) the very narrow and provincial "approved" sources Mormons would select to find their content;
(4) the complete lack of procedural and aesthetic flexibility, which limits creativity, vibrance and freedom of expression ("reverence" has benefits and its time and place, but IMO the Mormon version unduly limits expression, humor, passion, life, etc. in talks, lessons, musical presentations, etc.);
(5) the "democracy" of lay participation (I admit there are countering virtues to be extolled here and an often beautiful aspect that comes from shared humanity, simplicity, innocence, etc.) regardless of ability, skills, merit, personality, social intelligence, knowledge, desire to speak, etc.;
(6) the frequent use of the pulpit as a power structure, authority reinforcement mechanism, self-aggrandizement vehicle, etc.;
(7) the quantity and quality of Mormon preparation time for public "speaking" assignments is often pathetic; and
(8) although this post has focused on why Mormon talks and lessons suck from a TBM standpoint, I would be remiss if I did not acknowledge ;) that they also suck because much of Mormon doctrine and content sucks.
These are just a few thoughts off the top of my head on a Saturday morning. I could go on for a couple of hours if I thought about it. In summary, the Church does an ABYSMAL job on this topic.