You've offered quite a few opinions here going in a lot of different directions.. I want to address each claim/opinion on it's own merit.
With all due respect, your opinions and recommendations to the OP on what would be the best arrow build for his upcoming plainsgame hunt doesn't really carry a lot of weight considering that you yourself have no practical experience with bowhunting for African plainsgame or any other larger game animals. That advice is best left to folks with experience in hunting African plainsgame.
You can choose to believe or not believe anything you like, but you should base those beliefs on factual experience, and not what you feel or what you have read.. I don't base my opinions solely upon Ashby's findings or any other single data source. I base them on multiple sources with Ashby's findings and theories being a significant part simply because they have proven to be true in the field on live game animals in real hunting situations from my own experiences.
This is worth repeating because it is so significantly true where penetration is concerned.. As Ashby correctly states, "Even with every other penetration-enhancing factor in place, greater arrow mass still equates to more usable force, and more outcome-penetration".
Here is an easy, simple experiment that you can do right now that will prove this beyond all doubt... With this experiment, you can set aside all of the so-called more significant factors and simply focus on determining whether or not greater arrow mass and higher FOC will result in greater penetration.
To best demonstrate this, use a bow with a draw weight of 60lbs or less. The lighter the draw weight, the more significant the difference in penetration will be. Utilize two identical arrows that have the same exact shaft, spine, fletches, ect.. Screw a 200-300gr field point onto one arrow and a 100gr field point onto another. Shoot them both into the exact same target medium at the same distance as many times as you deem necessary.. I absolutely guarantee you that the heavier arrow will penetrate significantly farther into that target than the lighter arrow 100 out of 100 times. Furthermore, the heavier arrow will only continue to penetrate farther as the total arrow weight and FOC are increased up to that optimum level of the bell curve where arrow weight overtakes kinetic energy and the level begins to fall. However, that peak of the curve will be substantially heavier than most are prepared to believe..
In making this statement, you are ignoring significant parts of the equation that may facilitate this which are draw weight, draw length, and broadhead design just to name a few of the most critical considerations.. If they are indeed getting consistent pass-thrus, chances are they are shooting 65+ pounds of draw and have a 27" or greater draw length, and NOT shooting an expandable broadhead.
Just as many if not more elk, moose, or whatever other species you care to name are lost with arrows in the 400-500gr range because the overall combination of bow, arrow, and broadhead are all, or in part, insufficient to create enough momentum for effective penetration. As I have said many times in this and other similar threads, hunter's who are capable of shooting higher poundages and longer draw lengths have exponentially higher mechanical advantages over hunters who shoot lower poundages and shorter draw lengths. Those mechanical advantages allows them to make up for momentum lost due to friction created by poor broadhead choices or momentum lost from shooting lighter arrows.
To exemplify this watch ANY hunting show on TV today where a hunter is using a low poundage compound bow and a shorter draw length and 9 times out of 10 you will see the result is half or less of the arrow sticking out of the side of the animal as it runs off. This is a direct result of too light of an arrow likely paired with the absolute wrong broadhead. I hate to cite specific examples, but this is blatantly apparent with many of the "celebrity" female hunters who shoot light poundages with expandable broadheads. Ironically, they don't need to shoot more poundage to get better penetration... They only need to shoot a heavier arrow with the right broadhead.
The vast majority of technological advances in bows have come in the form of improved draw cycles, & let-off options, vibration reduction, and consistency. The truth is that the level of kinetic energy they are capable of producing has remained relatively the same since compound bows have been invented. You still have to be able to draw 70lbs of weight at some point in the draw cycle to shoot a 70lb. bow today just as you did in the late 1960's. How that weight is distributed across the draw cycle and how it's stored at full draw is what has changed significantly with modern bows.. This is precisely why the greatest advancements in bowhunting have come not in the form of the bow's technology per se, but in the form of better understanding of the physics behind arrow flight and smarter use of that momentum.
You are correct that testing is not hunting.. My advice offered here to the OP doesn't come from Ashby's testing or findings.. It comes from 40+ years of bowhunting and the successful taking of hundreds of animals species from all over this planet. But, it mostly comes from the unfortunate handful of lost animals over those same years, and by the lessons learned and applied toward improving equipment and techniques to be as effective as possible. I know what works in Africa, because I ALSO KNOW WHAT DOESN'T..
You are of course free to have any opinions that you like, but you would be better served to offer them based on factual experience rather than what you would like to be true.