I used to use a lot of moderate velocity cartridges, and from my experience with bullets impacting at 3500+ fps it adds significantly to lethality. Either cup and core or, mono.
That's interesting when time and time again we see guys talk about lead core bullets and that they "splash", "disintegrate", "explode", etc impacting at those velocities, or even slower than that. I do not subscribe to that line of thinking though.
What would be "your" obvious reasons, and why would it be illogical, or unfair?
The obvious reasons are that many hunters tend to unknowingly pick a version of a lead core bullet that will not hold up adequately when impacting that fast, or at least not be reliable and consistent. That said, more and more are figuring that out all the time and I think many now do fully understand the chances of over-expansion and shallow penetration are greatest in that scenario with certain lead core bullets. We see more and more short action cartridges being used now, with high BC and heavy for caliber lead core bullets that produce emphatic results at short and long range.
Some guys go with a smaller and slower pushing cartridge, others go for a stronger bullet like a mono.
Most monos still perform best at high impact velocities. Some have higher BCs that allow them to retain more velocity, even starting out a bit slower from a smaller cartridge. That means they still impact at a sufficient speed. That's another reason BC can be quite important. It can increase the capability of smaller cartridges, particularly with monos.
Here's something to think about: Hunting deer here where I live, it's most common to shoot them from a ground blind, box blind, or tree stand. Distances are typically 200 yards and in, and the vast majority are 20-70 yards at the most. I and a few friends do hunt fields where we've taken deer and coyotes to over 1200 yards, it's just not common at all.
A guy that buys a 300 RUM, 28 Nosler, 338LM, etc to hunt like that may be lacking knowledge or awareness to begin with. And then when he uses a standard lead core bullet, and blows the deer apart, he tends to blame the bullet.
Then, if that guy switches to a mono and sees less damage, he now says, "wow, these copper bullets are way better". He may think copper bullets are now superior to lead.
It's flawed logic though. It wasn't that the lead core was a bad design. It's that he was asking something ridiculous from it, and he likely picked a poor version as well. I was once that guy. I'll fully admit it. I had to clear my head.
The fact that the mono does less damage in that scenario tells us it's actually inferior in many ways (not saying overall) to how much trauma it produces. It tells us trauma and damage would likely only get much less as impact velocity lowers. The lead core would only get better, as it balances out more regarding expansion vs penetration. So now in that scenario, the results are flip flopped. So now do we say the lead core is superior? Some would, some wouldn't. Some would say that while the copper still can work at low velocities, it makes it overall more capable and superior. Perspective and preference really start taking ahold of the viewpoint and conclusions.
But there's way more to it. It's not that simple. And when we start comparing reliability, how to get a lead core to still work at high impact velocities, how lead cores can work reliably to way lower impact velocities, they have a longer overall range, can be highly effective from smaller cartridges even at long range, they cost way less, etc, etc. we can also say lead cores are superior.
Both people may feel they're correct. Since both types of bullets have their strengths and weaknesses, and both have different designs and mechanisms, it's unfair to say as a whole one is truly superior over the other. When you compare scenarios that are highly mismatched, it is unfair. There are many different types of monos. There are many different types of lead cores. Picking a different kind of either can change the outcome of certain scenarios.
So I say it's illogical and unfair to say a copper mono is superior to lead core bullets simply because you can push them so fast and get good results, where certain lead cores may not do so well. Since monos work best at high speeds, it stands to reason pushing them that fast from the start would be ok, especially if their BC is on the low end. The higher the MV, the more it compensates for that.
A lead core, being more dense and capable of being pushed slower from the start, while still being stable and retaining plenty of velocity, makes them not even need to be pushed so fast, especially if the BC is high.
I ultimately see it as which one is more superior is based on the particular scenario and what you're asking of the bullet. A certain mono may be the superior choice in that scenario. A certain lead core might be the superior choice in a different scenario. To say one overall is superior over the other I do believe is unfair and illogical.
I don't know if that answered your questions. My brain is fried after a long day. I may have to come back later and reattempt after I recover lol.
I say all the above with utmost respect and mean no offense to anyone. Please don't read too far into my scenarios and examples and think I'm picking on anyone or talking down about anyone. It's just the best way I could think to get my point across. I have nothing against what cartridges anyone uses if even why. I'd just love to see everyone succeed and have the knowledge and resources to do that without being inundated with misinformation or personal preferences being pushed upon them as fact and what they should do or use.
If a mono is the best choice for how you hunt, get a great one and good luck to you out there. If a lead core is the best choice, get a great one and good luck to you out there.