Wilder’s résumé is aging like a fine wine

You don't understand the concept. If you thought Wilder's opponents were terrible but they went on to beat guys who they were not expected to beat, the record could only age well.

 

"Unfortunate circumstances"

What utter BS. If Wilder had injured his shoulder and quit or had his face badly cut and got stopped, you wouldn't be making these excuses for him. Having better physical health is a clear advantage in combat sports and if you're less willing to quit (whether it's the right choice from a health perspective or not) then you'll stay undefeated for longer. Vitali's biggest advantage over Wilder is skill, he's a much better technical boxer. But Wilder is a vastly bigger puncher and that attribute will serve you better against many opponents. Wilder is also faster and longer than Vitali and most other SHW's, so "not landing his shot" hadn't been a problem for him in his career. If Wilder can land on a defensively-orientated Fury, he can land on anyone he fights and almost none have Fury's powers of recovery.

"Every fighter matches up differently"

Yes, and Ruiz wouldn't match well with Stiverne's style. Stiverne wouldn't trade with Ruiz as AJ did, he would school him on the backfoot with his height, reach and power advantage as he did prime Arreola. 40+ retired Arreola had never been a backfoot boxer, couldn't do it to the longer, more skilled Stiverne but was able to have a lot of success against Ruiz. And Ruiz's chin has been overestimated: he was dropped early by AJ, dropped earlier and hurt multiple times by Arreola. Stiverne would have more than enough power to hurt and drop Ruiz, which would keep Ruiz hesitant to engage like Arreola 1, or KO'd if he became overzealous like Arreola 2.

"apart from his win over Helenius, he was a career Euro level fighter"

Aside from Ruiz's win over AJ, he's been a career Euro level fighter. A Euro level fighter with size, chin, relentlessness and heart would have a decent chance of drowning AJ on an off-night. We saw it at a lower level with Puritty against a young Wlad. You don't need big power to hurt/drop/concuss AJ and he can be demoralised, made to quit.

 

Wach was one of Wlad's top 10 challengers of his 9+ year reign. Many of Wlad's defences were considerably worse than Washington and Szpilka (who beat Wach).

Duhaupas wasn't a serious threat to Wilder because Wilder had good durability, heart and engine. Ruiz was a legit threat to AJ because AJ didn't have Wilder's durability, heart or engine. Wlad isn't the best example because his first loss was to a poor man's Duhaupas in Puritty.

 

Duhaupas KO'd Helenius, who was being groomed as a top contender in the Klitschko era.

 

"Vitali was clearly a much better fighter than Wilder though, irrespective of his thin resume."

Vitali was clearly much more skilled than Wilder but Wilder is clearly much more powerful, longer and probably a lot faster (Wlad said that Wilder was extremely fast twice in the same sentence when asked about Wilder-AJ in 2018 and Wilder claimed that Wlad told him he was the fastest heavyweight he'd even been in a ring with).

If you can level your opponent with one shot at any time, that makes up for a lot of technical deficiencies. And when you have great speed, length and toughness (mental and physical) to add to that equation among other things, you become a H2H nightmare.

"if Stiverne hadn’t been one of Wilder’s better wins, you wouldn’t even mention him...Ruiz IS a world class HW"

If Ruiz hadn't have had a Buster Douglas night against a vulnerable champ in AJ, no one would regard him as anything more than a fringe contender. Ross Puritty didn't become a "world class HW" just because he beat Wlad. Ruiz's 2nd most impressive performance is losing a controversial MD to Parker in NZ but Parker also has controversial MD's and SD's against Hughie and Chisora: are they also "world class HW's"? Aside from that it's competitive 10 and 12 round fights against washed up versions of Liakhovich, Kevin and Arreola. The mutual opponent of note is Arreola, who Stiverne was able to both school and brutally KO in his prime, displaying more to his overall game than I've seen from Ruiz.