I guess I should probably elaborate on my terse thoughts about how I'm glad the Streak ended to provide the counterpoint since the other side has been discussed, and quite frankly, I'm bored and it's something to do.
First thing I'll say is that Undertaker continuing to wrestle after XXVIII never made much sense to me. I guess it'd be a little odd if his final moments were sort of group thing and the WM 33 ending definitely would've been more fitting, but the End of an Era Hell in a Cell match seemed like a more natural stopping point, and it's one of my favourite matches of all-time. I remember watching it live with my friend & father, dad wanted Taker to lose, friend wanted Taker to win. They hit Taker with the Superkick/Pedigree combo and it was fun to watch as my father pre-emptively celebrated and my friend was freaking out that Taker was going lose and I sat there snickering at them because "He's going to kick out". I am a prick.
But I tell that story because I do love that the Streak happened obviously, and that four year angle is perhaps my favourite storyline in WWE history. It felt grand, and to be honest, even though Punk is probably my favourite wrestler ever, his feud with Taker for the Streak felt perfunctory. "We need someone to fight Undertaker, and Punk's not doing anything, we sure as hell can't let him main event when we could just do the same main event as last year instead!" He won the opportunity in a fatal four way like it was a number one contender's belt for a championship, it sucks but Bearer's death was the only thing that gave that feud any texture. It mostly just felt like another notch in Taker's belt. And not that I ever went into a Taker Mania match expecting him to lose, but the Streak itself never carried much weight to me on it's own. That's why the WM 23-XXVIII were the peak of the Streak for me, who really cared about the Streak when he was fighting Mark Henry?
Mostly though, I just don't see the benefit of Undertaker retiring with a 27-0 WrestleMania streak. What benefit is there that doesn't already exist? It's a more impressive record but it's not like the Streak is something so flimsy that a lose truly invalidates it's prestige. Taker still went 21-0, a feat that will literally never be repeated again, absolutely historic. 25-2 is again, the greatest record in WrestleMania history, and it just won't ever get topped. The two losses do take away a bit of the aura for sure but it's still widely beloved and cherished part of wrestling history. I don't think that changes from it being broken. If anything, it probably strengthened fan reception to it, there's evidence of that in this thread.
Look, I haven't seen Lesnar vs. Taker but I've seen the three count. I've seen the fan reaction, I've seen that "Yes" guy a million times on the internet since that monumental event. That experience alone, justifies the Streak being broken. A lot of people value crowd reaction as an integral part of the wrestling experience, and there's probably something similar to the atmosphere of Taker losing at Mania, maybe when Bruno finally lost, but it's definitely a rare occurrence. I totally understand trading the guy who broke the Streak, I don't think it should've been Lesnar either but I can't understand trading that atmosphere and experience just so the feathers in Taker's cap would be fluffier.
Finally, streaks and records are meant to be broken. If Taker retired undefeated, the Streak would've felt incomplete to me. But I also believe when you retire you go out on your back, so I still have a bone to pick with Taker I guess lol. Honestly though, if anyone's earned the right to leave with their hand held high, it's Undertaker, so that doesn't bother me much. I also got my wish about him losing the Streak, albeit in a very Monkey's Paw way, so I can't complain too much about.
I'll just reiterate will quickly, I'm not saying Brock should've ended it but I definitely think it was better to have Taker's streak be broken at some point rather than retired undefeated.