I've never had leg issues with my keets or turkey poults in my brooders (and with as many as I hatch, things can/do get pretty crowded at times), when/if I ever see leg issues it is usually only from hard hatches/breeches or temp fluctuations during incubation, before they've even ingested any starter feed or get moved to the brooders. (I don't consider slipped tendon to be a protein related issue, IMO/IME, if it's not from a genetic defect, it's caused by a nutritional deficiency, or from an injury).
As for high protein causing issues for Turkeys... I have 6 healthy adult Turkeys that were raised on 30% game bird feed up until 6-8 wks, then weaned to a 24% game bird diet from then on until I started fermenting my feed for them (but still staying in the 22-24% protein range for them), they also were fed some catfish diet pellets (32% protein) mixed into their diet as a supplement prior to breeding/laying season... they are all now breeding and producing like crazy. No leg issues on any of my 6 adults. They are Heritage varieties tho (and they free range daily), not the broad breasted beast varieties that are extra prone to suffering leg issues at a young age due to how rapidly they put on meat/weigh anyway. I also have over 100 poults that I have hatched from their eggs this season that are also being raised on a high protein Game Bird starter, supplemented with Ultra Kibble... plus they also get mealworms, scrambled or boiled egg and minced raw organ meats on a regular basis for treats. Even with all that excess protein, they suffer no leg issues as of yet, (ages range from 9 weeks of age down to a few days old so far).
While I agree in cramped/overcrowded brooder conditions keets (and poults) may not need 30% protein because they can't burn it all off, I'd be more inclined to think/believe leg issues are caused by either too much or too little of a different ingredient/nutrient in the feed, not the protein % content itself. Back when I first got into Guineas, all the info I found about excess protein stated that it was typically just passed by the bird without causing any issues (not sure when that theory changed). Or maybe it's the actual different types of protein or the quality of the protein sources themselves that's used in feeds these days. As we all know, not all starter feeds are created equal, especially with so much GMO garbage being used in poultry/livestock feed nowadays... but I have raised keets on 25% protein starter before, and I hated it. The keets were puny, starving all of the time, they started cannibalizing each other's ceres, were major feather eaters once everybody started going thru their first juvenile molt and always had a more pronounced keel bone, etc. Even now, what few birds I kept out of those batches... are still smaller as adults than my higher protein raised keets matured out at. And hen I processed a couple of them, they had excess internal fat... and they were males.
So I personally will never again revert to lower protein diet for my keets... but best of luck with however you choose to feed your keets. And no offense meant to you, your opinions, your research or the speakers at the conference, but I think for the sake of healthy keets/birds and my reputation as being someone that produces and sells healthy keets/birds... I'll stick with suggesting the feeding recommendations from experienced Guinea Fowl/Game Birds breeders like The Guinea Farm (28-30%) and Shady Hollow Farm ("the higher the better"). There's also an exotic Guinea Fowl breeder that posts here who feeds all of his breeds of Guineas high protein as well, (supplementing with catfish diet pellets, which from reading his posts is where I first learned about using them). I've never seen him mention any leg issues from high protein.
So again, best of luck raising your keets on lower protein feed. Hopefully your keets/Guineas don't ever experience any of the lower protein diet issues that I've mentioned.