His absolute STOMPING of John Cena at SummerSlam 2014 contained sixteen snap suplexes (fifteen of them Germans). This counts brilliantly both for injury and for insult.
For insult: the suplex, especially the German suplex, is a traditional wrestling move. John Cena's wrestling skills, rightfully or not, are perceived as being grossly below-standard for someone standing at the top of the business for as long as he has. Subjecting Cena to an assault of suplexes in a meta sense mocks Cena for his limited ability, and specifically the lack of variation in his signature match formula. Furthermore… If Brock intended the exact numbers, sixteen also mirrors the number of World Heavyweight Championships that are officially counted as part of Ric Flair's record, while fifteen is the amount of world titles John Cena has. Throwing shade at the idea that Cena could potentially break said record in the future seems like exactly something Brock would do, as he has stated on numerous occasions his belief that Cena's position in the company was only ever made possible by his own departure.
For injury: Cena is notorious among smarks for often bumping on his butt as opposed to his back. A creative mind could use this to explain Cena's Superman-esque pain threshold by saying he's mastered a way to absorb his pain by protecting his back. Suplexes are designed to drop the recipient on either their upper back or, in the case of forcefully-applied rear suplexes such as the German, the back of their neck. With Lesnar being a physical genius in the art of wrestling and dishing out pain and Heyman a mental mastermind, they very well could've noticed this and decided to intentionally spam Cena with a powerful move that he could not protect his back from.
The combat pragmatism only increases when you look at the rest of Lesnar's offense. John Cena is one of several individuals who tend to take the F-5 directly on their side instead of their front. After hitting Cena with an F-5 thirty seconds into the match, only for Cena to kick out, Lesnar would repeatedly punish Cena with knee strikes to the side of his ribs, the aforementioned suplexes, and mount punches and facewashing kicks/stomps aimed generally right for his head. Every point of attack was designed to punish John Cena by making it ever that much harder for him to push himself to stand. This not only ensured that a second F-5 would be enough to finish him off, but limited his flurries of life to short bursts which would all fade within seconds, allowing Brock to easily put them out with one or two actions.
Brock's ability to tank FOUR spears from Roman Reigns in their Wrestlemania 34 rematch (even taking into account the fact that it's Brock friggin' Lesnar) makes a lot of sense when you remember he spent much of the 2016-17 wrestling year going up against Goldberg, and basically lost his title the last time from Goldberg's Spear kayfabe injuring his ribs and diaphragm. Between the loss to Goldberg and the fact that Reigns came pretty close to beating him on one occasion, Brock's training regimen over the last couple of years probably involved building up his resistance to that exact attack.
Lesnar's new MMA-style finisher, the Kimura Lock, is either a case of Fridge Brilliance or Fridge Logic depending on one's interpretation. Brock Lesnar is an accomplished amateur wrestler, and overall, the sport of wrestling requires that a person be good at controlling their opponent while on top of them. As a result, many wrestlers in MMA are more comfortable in top position than bottom, so it seems odd that Lesnar would use a move (the Kimura) that requires him to be on his back, which is an advantageous position for his opponent and a less advantageous position for himself, as opposed to maybe an Arm Triangle, where he could control his opponent from top position.
However, it could be argued that during his time as a professional mixed martial artist, Brock's Brazilian Jiu-Jitsu skills (which require a fighter to defend and/or create offense while on his back) improved to the point that he saw it as a way to gain an edge over other wrestlers. He also may have seen the success that Undertaker had with his Hell's Gate finisher (a Gogoplata, performed on one's own back), and adopted a similar submission move for himself.
Ever since "Suplex City" was born, Lesnar has a reputation of putting on repetitive, boring, predictable matches. However, prior to his 2004 departure from WWE, Lesnar was known for being somewhat of a showman. He used a Shooting Star Press in at least two different matches, utilized superplexes, and even during his entrance, he would show off his athleticism by leaping onto the ring apron from the floor (which he still does occasionally).
At WrestleMania 19, Lesnar took a hard fall on an attempted Shooting Star Press, and at 2012's Extreme Rules pay-per-view, Lesnar attempted a flying attack on John Cena by using the steel ring steps as a diving board, and Brock ate a chain-wrapped fist to the face for his trouble. Ever since then, perhaps because of those events, Lesnar has abandoned almost all traces of showmanship during his matches in favor of brutal, laser-focused precision, and he's been unstoppable ever since.
It gets worse: On top of his history of neck problems (including the injury that made him give up the WWE Championship), after his eventual retirement, it was discovered that Bryan had suffered multiple undiagnosed concussions through his career. The German suplex in particular targets the neck and the back of the head. Do the math. Add to it the horrifying ending of Lesnar's match with Randy Orton at SummerSlam 2016 and it would probably not be an exaggeration to say that WWE avoided a tragedy.
, where he could control his opponent from top position. 