I'm deliberately putting my response to the second part to avoid a wall-o-text since it is more historically fastidious:
The only centers to lead to their teams to multiple titles in the past 40 years are Shaq, Hakeem, and Kareem. Both Shaq and Kareem needed top 10 all time great guards to do it. And Hakeem had a top 5 shooting guard of all time for his second title. Outside of those 3 the only other center to lead his team to a title was Moses Malone...who also had an all time great teammate and borderline superteam supporting him.
The fact is there have only been a handful of centers to actual lead their teams to multiple titles. So to hold this current crop of bigs to an unrealistic standard not even the bigs of yesteryear reached is a bit unfair.
Towns, Embiid, and Cousins are the only 5 star...mvp caliber centers in the league. However, the league is filled with capable centers with valuable specialized skills sets. Considering how bad the 2000s was in terms of centers this decade has been a massive improvement.
Is there some reason you're forgetting that Anthony Davis exists? I thought you were restricting yourself to "Rising Star" centers or thereabouts, but you keep talking about Cousins, so that hardly makes sense.
Make it 42 years to cover the modern era. First, you're wrong. We're talking classic bigs, not just centers, so guys like Tim Duncan needs to be added to that list. Okay, let's dig in.
Since we went back to the ABA-NBA merger, our first championship is headed by PF/C Bill Walton's Trailblazers. The very next year? 6'9" PF/C Elvin Haryes and his Bullets. Who unseated them in the Finals the following year? Center Jack Sikma's Sonics. See a pattern?
Meanwhile, while they needed guards, if you look at these "small" guys who disrupted this, and dominated as alphas in the 80's, that would be the 6'9" Magic/Larry, and they always had league-dominating classic bigs as their main sidekicks (Old-KAJ/Parrish/McHale). KAJ was still in full alpha mode when 1980 took off, the year after Sikma's crown, with rookie Magic aboard, to collect their first ring together. In Magic's case, he depended on this "sidekick", the greatest center in history, to produce the majority of his team's scoring up until 1986-87. Thought a Kobe nuthugger might find that interesting.
The Bad Boys were a team dynamic. Thomas was the Captain, no doubt, but Laimbeer was a defensive specialist and enforcer who both scored and rebounded better than Gobert, for example, while Rodman was the greatest rebounder in history. Still, we'll give that to smalls: Thomas/Dumars.
That brings us to the 90's which outside of Jordan were dominated by classic big men: Olajuwon & Robinson (Ewing/Shaq were Jordan's punching bags). Jordan was the earthquake who inspired all this to change. He was the only guard--
Chicago the only dynasty-- in modern NBA history prior to the rise of Downtown Moneyball that didn't need a truly great big man to reign.
Nevertheless, Shaq & Duncan succeeded him in owning the league. During their reign, Detroit squeezed in another defense-centered team concept championship, but this time with their defensive MVP being their center, in Ben Wallace, not a guard like Dumars, and he was as small as classic big men come. Miami also squeezed in an outlier behind Wade-- perhaps the only guy besides Jordan to do it without a great big even if only once.
Boston got theirs, but while most perceive Paul Pierce as the leader of that team, Garnett was easily the greater player, and unsurprisingly the one who produced both more Win Shares and a higher VORP in their championship season. Pierce got all the attention because he was a crunchtime scorer.
Finally we arrive at alpha Kobe, but Kobe needed Hall-of-Fame lock Pau Gasol to win his back-to-backs. That was the end of the dominant big man.
Is anyone fretting for Golden State, Houston, Toronto, or Cleveland today because they don't have a great big man? Everything rides on Unibrow.