Well, I dunno. Riders in the Showa era were flawed as hell, but those flaws are almost always portrayed as something that one overcomes as part of being the hero- which isn't really that different now. By the end, yeah, the Showa Riders may be these idealized, unquestionably-good characters, but they still have to work to get there. Often times being a Rider IS inherently a flaw, even. Again, not that much different.
Hongo and Ichimonji, in the beginning, were not happy with what had been done to them. They had to learn to deal with what they'd been made into, and a couple times have to overcome their own personal hurdles to be better heroes. Even if they're out-and-out good guys, the show doesn't forget that being a Rider also kinda sucks and there's no going back for them. Almost every Rider show since has touched on this.
Watching early V3 again, I think Kazami is faaaaar from the jovial post-Zubat way Miyauchi has played it ever since (emphasis on post-Zubat, since I think that had something to do with it.) He's kinda got a ruthless streak, and it actually bites him back a couple times. He's not really a friendly guy. People said Accel was like a new spin on V3, and you know what? They were right! The "you killed my family" thing is not the most original idea ever, but both characters stuck to a similar version of it. A quest for vengeance gives way to something bigger.
Yuuki's problems basically need no explanation, but I think it's especially interesting that the show is also not afraid to show Kazami in a negative light in regards to how he deals with Yuuki, who himself has got a lot of wrong ideas in the beginning. I find myself siding with Riderman a few times, even if he's "wrong". The interaction between them is on par with anything in the Heisei era, IMHO. I think the Gills/G3 relationship towards the end of Agito is almost a direct descendant of it.
With Jin, where do I start? X-Rider may be the hero of his show but it was not afraid to show he could be a pretty lousy hero at times, particularly early on (and I like that he gets better at it.) Episode 8 is startling because X basically loses- he still defeats the monster and rides off at the end, but the show almost asks "so what?"
Amazon had culture shock to the extreme, being an alien in his own homeland- we've yet to see a Heisei series really touch on that idea again, though there's elements of it in Decade (of course.) And even Fourze, though it's played entirely for laughs there, but I get that vibe. I like that Amazon dealt with issues completely removed from the fact that he was a Rider fighting bad guys, though they still tie into the story and his role in it- he has problems just trying to communicate at first.
Shigeru, I think the show was pretty clever with how it makes him seem like a much more straightforward, idealized character than he really is, then it tears him down in episode 30 only to build him back up by the end. There's a nifty subtlety to it. For such a loud, wacky show, it's often working on another level beyond "Stronger just kicked that guy's head off". I still wish it'd gone to the original 50-something episodes, because it sounded like there might have been some interesting stuff.
I think Tsukuba is unique in that while he starts out like a seemingly "perfect" hero, we start to see parts of it chip away so that by the end, he's basically where Kazami was at the beginning- a lot more ruthless and angry, given how dire things are. He's a bit unhinged in the finale! Definitely saw that in Kenzaki and Eiji, except in the latter case things turned out better than the other two. I like all that.
Oki is probably the most straightforward "goody-goody" Rider of the era and even he had a literal mountain of things to overcome. There's a two-parter early on that I thought defines his character perfectly. I think a lot of his flaws are things he sees in himself, but they have consequences for others as well.
Murasame, well, he only had 45 minutes, but I think Spirits took a lot of the stuff only hinted at or shown briefly and has expounded upon it to make him one of the most complex Riders in the whole 40-year history. Even as a hero, he is not perfect by any means, even if Badan says otherwise.
Minami's problems in BLACK are almost entirely derived from the plot itself and his relation to the villains, but that's not really anything new, and it's not that much different from the flaws of Riders in the Heisei era. The hero's flaws should always derive from the plot to a degree, or work towards something in the plot. It'd just seem weird otherwise. Like would it really be a good idea to make Godai an alcoholic or Tendou snort cocaine if it didn't factor into the story at all? Well, on second thought...
I think the big difference now is with more Riders running around, there's another level of complexity, which is fine, but underneath that it still boils down to "Kamen Rider is the hero, he's got problems but he overcomes them and wins in the end." For everything that has changed since 1971, there's a lot more that hasn't.
(Sorry for that tangent. Back to Fourze.)