In 2006 Werdum was in his 20s and a top 7 HW who after losing to Nog went 6-2 in his next 8 fights and mounted wins over Fedor, Aleks E, Bigfoot, Gonzaga and Brandon Vera in that span. I don't see how that's worse than beating 39 year old Werdum who went 4-5 in his next 9 fights.
I'd also argue that beating Sergei when he was in his 20s with a record of 10-1 was superior to beating 37 year old Arlovski, washed up CTE JDS or 37 year old Reem who had already been knocked out in the UFC 3x by the time Stipe fought him. When Nog fought Sergei he had never been knocked out and sure, he wasn't as "accomplished" but he was in his absolute peak form.
Same thing goes for Barnett. After losing to Big Nog, Barnett was at his absolute peak form and went 9-1 in his next 10 fights and went on absolute tear. Id rank this win higher than beating washed up CTE JDS who went 1-6 in his next 7 after losing to Stipe or 39 year old Werdum who went 4-5 after losing to Stipe.
For me personally beating a high level HW at their absolute peak right before they go on a great run is more impressive than beating an "accomplished" HW who's on the doorstep of 40 years old and retirement with no significant wins after losing to Stipe.
I agree Ngannou is one of Stipes best wins but he was clearly green. He lost to Derrick Lewis in his very next fight and that says a lot. It's no coincidence that a more seasoned Ngannou sent Stipe to the shadow realm in the rematch. It's no coincidence that when JDS still had some of his prime left even post Cain beatings, he still out classed prime Stipe. Stipe never did well when he fought great HWs in their peak form, Nog on the contrary did.
And yea it's not just the wins. In his first 3 years of fighting Stipe was 9-1 with an embarrassing loss to Stefan Struve. In Big Nogs first 3 years of fighting he was 19-1 and arguably undefeated with the loss being a robbery against Hendo in RINGS which he avenged via finish. Nog was way more active early on and never lost to Struve level fighter when he was young AND he went on to beat great HWs at their peak and in their 20s. Stipe can't say he did the same.
Again I hespect of Stipe and rank him as a top 5-6 HW of all time. Maybe 5 if you rank JDS below him but good arguments can be made for JDS being ranked above Stipe based on his wins over prime Cain and younger Werdum but I wouldn't be mad if someone ranked Stipe over him either.
At the end of the day it comes down to what you value more: beating and old and accomplished fighter who's either washed up or close to being washed up or beating a less accomplished fighter who's very good and who's in his peak form and goes on a nice run after.
For me it's the latter.
Peace King.
You bring up a good point, particularly about a fighter going on a good winning streak after and hitting their prime, but I don't think it really applies to Werdum. After the Nog loss he was up and down. He had some solid wins, but also had some loses, he was basically a 500 fighter before he came to SF between 2006 to 2009. Now, it was in 2009 that Werdum really started to develop when he went to Chute Boxe and worked his MT which became a big part of his game and then Kings MMA. And that's when he hit his prime around 2009/2010. But Werdum in 2006 wasn't that guy yet, that winning streak you mention started about 3 years after the Nog loss.
So I can't value beating Werdum in 2006 close to beating him in 2016. I can't because at the time in 2016 Werdum was the #1 HW in the world and UFC champion, regardless of age, he was at the highest point in his career. In 2006 he was a top 10 HW that the next 3 years went 3-2. Now if you ask me Werdum in 2016 vs Werdum 2011? Different story, I would say the wins would be much closer.
I think your point is there more with Cro Cop, cause after the Nog loss he did very well aside a flukey KO loss to Randleman and losing to Fedor. He was in his prime at that point. Sergei was a good HW, but I don't think he really reached anything, it's a good top 10 win but Sergei was very up and down. I think in 2004 Nog fought prime Sergei, I just don't think Sergei was really elite. Barnett was elite, I think it's Nog's best win IMO.
So overall you do have a good point about beating a fighter that's about to hit their peak and go on a great run as a high win, I like the point in general. I just don't think it applies to those Nog wins. Not for Werdum or Sergei, Cro Cop yes, Barnett was elite. Randy and Tim were falling off after, but still very good wins.
About the activity, Nog was actually 15-1 in his first 3 years and Stipe was 9-1, so Nog had 6 more fights. But all to do with fighting in Grand Prix tournaments. Nog fought 2x in a night in his first Rings GP and 3x in a night in the Rings GP he won. So those extra 6 fights he had, he was fighting multiple times in night. So I don't think he was much more active than Stipe, close to the same.