Getting back to the OP..
Have expanding bullets finally made big bullets obsolete?
I say, no. They haven't made big bullets obsolete. I think a more applicable question would be "have expanding bullets finally made smaller calibers a viable choice for self defense?"
And to that, I will say, generally, yes. Today, with the "good stuff".
Every JHP bullet in the world isn't equal. The best are really good today, but that wasn't always the case. Probably a number of you here today weren't shooting pistols in the 70s, when Lee Jurras and his company Super Vel proved that the light (for caliber) JHP bullet moving fast (again, for caliber) COULD work.
I began shooting pistols when "duty caliber" factory ammo essentially came in two flavors, FMJ bullets for semi autos and lead bullets for revolvers. I remember articles expounding on how the .38 Special was actually superior to the 9mm Luger, because the lead bullet of the .38 would actually, sometimes, expand a bit. 9mm FMJ never did.
Some of us remember the pre-Internet, pre-JHP, pre-Glock, pre-wondernine era. We remember what the 9mm was (and still is when you use FMJ) and are amazed and impressed by what the 9mm JHP has become today. Much, much better, but not yet "perfection", unless you buy Austrian Kool-Aid.
The primary reason that the 9mm is the organizational caliber of choice isn't how well it works, as a cartridge, its because of how well it works in modern pistols, used to arm groups of people. People who you aren't going to train to the maximum level possible, only the needed level to meet your qualification standards. NO group, LEO or military has ever trained its members any more than what was considered the necessary minimum standards.
What caliber (and what gun) that the military and the police use is NOT chosen by the "foot soldiers". It is often a more political than a practical matter, and sometimes, it is entirely a political matter.
The US military didn't "abandon" the .45 caliber because of any practical reason, replacing the .45 in the 1980s was a political matter. We made a deal, back in the 50s, with NATO. We were pushing NATO to adopt our new rifle round (7.62x51mm), and they didn't want to. (expense was the usually cited reason), so, we made a deal, if they would adopt our rifle round as the new NATO standard, we would, when the time came to replace our 1911A1s, the replacement would be in "their" 9mm caliber. NATO agreed, but were not happy campers about what followed.
Because, #1, barely a handful of years later, (and another political decision) we adopted the 5.56mm round. And, #2, it took us nearly 30 years after that deal was made to decide to replace our aging inventory of 1911A1s.
They did adopt our 7.62 and decades later, we did keep our end of the bargain, adopting their 9mm as our military round.
Do note that while there were a handful of exceptions, our LEOs didn't adopt the 9mm round until AFTER it was adopted by the military. Our Police didn't give up their revolvers (by and large) for 9mm semis, until after it became our primary military pistol round. It wasn't wondernines, all by themselves, and it certainly wasn't the stellar performance of the 9mm round at the time (because at the time general 9mm performance wasn't as good as it has become today), it was because of the cost/benefits of using the same round as the federal government. YES, there were other factors, which assisted in making the decision, but I think the biggest factor was simply that the military and Federal police forces had switched to the 9mm.
Also note that, again, with a few exceptions, nobody had spent much effort trying to improve the performance of the 9mm, UNTIL about the time it was adopted by our military and police. For the first 70 some odd years of its use, very little was done to improve the terminal effectiveness of the 9mm Luger.
I do believe that the advances in bullet performance we have today came about only because of the fact that we (those in the position to make the decision) decided on the 9mm, and because of that, because we were going to use the 9mm, no matter what, we put serious effort into making it perform acceptably as a personal defense round.
AND, even so, those advances don't apply to our military, who are bound by the rules to use FMJ ammo, anyway.
)
)