In today's world where we have really good, controlled expansion bullets, like the Barnes TSX, TTSX, LRX or Swift A-Frames, are solids still required? We used solids when your other bullet offerings were mostly cup and core bullets that would blow apart.
We don't use solids because other bullet blow up or they are not good. Solids are the cheapest insurance policy you can buy, Solids can, and have saved the day many times..............
Conventional beliefs and thinking would dictate you use Solids for elephant, hippo and buffalo. There are those today that might be fooled into thinking that even for buffalo, solids are just not required.... I personally do not belong to that group.
Certainly no sane person would use conventional expanding bullets, or any trauma inflicting bullet on elephant.
Hippo on land, I like a solid for that, even though I have been forced once to use a trauma inflicting bullet, followed by solids, it worked out, but by choice I would have used nothing but solids.
Buffalo traditionally in years gone by, trauma inflicting or expanding bullet for that first shot, followed by solids. Some today believe that the conventional bullets, some of which you mention, are just so good these days, you don't need solids. I do not agree with that concept myself. With buffalo, after that first shot, if it is not DRT on the spot (and that is rare with buffalo) then its chaos and mayhem from the second that first shot is fired. If its a good shot, buffalo will hump and buck and run in some direction. There will be brush, trees, sticks limbs that will most likely be in the way, the second plus shots will not be like that first perfect shot, you may very well be shooting the south end of a north bound buffalo, and its a long way from one end to the other, and there is NO Trauma inflicting bullet or conventional expanding bullet that will penetrate from the ass end of a buffalo to its vitals, only a proper designed solid that will penetrate deep and straight can accomplish that mission.
Now of course you can be a ego driven newbie, and you can take that first shot with your perfect expanding bullet and just wait and see what happens..........After all, you are the best shot in todays world, and nothing can go wrong. You read all the right books, talked to all the right people and you obviously have everything under control, Right?............... Except for that damned little stick that was 5 feet in front of your target, that you did not see....... hmmmm......... or any number of a 1000 other scenarios that might make things go a little to one side or the other, what are you going to do now? You are so full of it, and just know that your Swift, X, Woodleigh or what have you is just so good, you did not even think about a solid, and now you have nothing that can solve your problem for you........... Oh well, you just lost a day in the field, or maybe you just lost your buffalo, or maybe worse, you got someone hurt or injured...........A good solid is good insurance and can save time, energy, dollars and even lives.........
I had always been traditional Expanding/trauma for first shot, and solids thereafter for buffalo. When I went to the field the first time with a prototype 50 B&M, using more conventional .500 caliber bullets available at the time, I decided it might be a good thing to backup some of these bullets with a solid of some sort. I had JD make up a few 400 gr Round Nose for that mission. Well it was a learning experience no doubt about it....... for all wildebeest, oryx, zebra, kudu and such animals, I used that little RN SOlid as backup, since I was not sure if those .500 caliber bullets at the time might fail, and I did not want to loose anything. Nor waste time, I was on a pure shooting/testing mission, I was not hunting, I was shooting........ I had tested everything before hand, so I got no real surprises with the conventional expanding, and I was using the same velocity that I had tested. But that sorry little RN SOlid did not do its job all the time, broadside shots on those animals did ok, but anything from the rear or the front would veer severely off course and many time exit 90 degrees, they were awful...... That is when I went to work on proper solids.
Speaking of conventional being so good......... many years ago I was in Zimbabwe with 458 Lott and 400 gr Woodleighs at or around 2400-2500 fps......... At 50 yards a nice impala stood, with its rear to me....... I took the shot, straight up the rear..... The poor thing look liked it nearly exploded from the rear, it was ugly, but it was not over, it was down of course, but the bullet did not make it to the vitals..... It had over expanded and did not penetrate enough. It was an ugly thing I will never forget, nor would I ever do again, not with an expanding bullet of any kind. Would a TSX or Swift made it, probably so........ but still, give me a solid, I know without doubt what that will do.
To each his own, from that early experience I started using solids to back up everything, not only buffalo, but everything larger than 250 lbs or so....... The thing is, things go wrong in the field, its not always the perfect shot like on the shooting range. I never quit shooting until the problem is solved, and then I shoot again anyway, or you are out of ammo, or you have no shot........ All my shots after #1 is going to be a solid, a properly designed solid, like we have been talking about, it might save the entire day of tracking, it might save the loss of an animal, or it might just save a hell of a lot more.
But to each their own, this is what I did, and what I adhere to now and in the future with any shooting endeavor I might undertake, you can do as you please.......
There are many many good reasons to have a Properly Designed Solid with you, and there are no good reasons not to..............