Yeah Punk was the longest reigning WWE Champion in the modern era which therefore made him the longest reigning world champion of it too bc no WHC had a longer reign.
Brock is the longest reigning universal champion ever obviously and now he's also the longest reigning world champion of this "modern era" and that's true whether WWE puts up a graphic saying so or not.
Are we not allowed to say Cena is a 16 time world champion? Do we have to specify how many reigns were WWE and how many were WHC?
I don't think even if there had been any comparable WHC reigns it wouldn't have mattered at all. Punk didn't care about having the longest world title reign, he was very specific about moving up the WWE Title reign records and WWE promoted it as such.
I would just say Brock Lesnar is the longest reigning Universal Champion and leave it at that. Not only is it title accurate, but you don't even have to qualify it with a time period as no one has been the Universal Champion for longer.
The only reason WWE mixes records from two different belts is because they want to stop talking about who held it before. Either Demolition or in this case CM Punk. There's no point in it. It's also something extremely new to WWE as they didn't used to make up these new records and push them. Just let people forget Punk existed, it'll happen eventually.
Now talking about how many titles someone has acquired is entirely different. You're not really comparing different records when you simply say wrestler A is a 2-time world champion and a 6-time tag team champion. It's just how you're describing their accolades, not records of different belts and different belt holders. I would say it gets more complicated when talking about Cena beating Flair's "record" of world titles, because then you're making it a record, but that's another topic for another day.