Yes no one is currently better than Reigns as the FOTC, but that's because for at least a decade WWE has ruined all other talent or booked them with indifference so the audience lost interest in them.
Ziggler, Wyatt, Barrett, Rhodes, Ambrose, McIntyre, Nakamura, Zayn, Owens, Rusev, Balor, Ryback, Joe, Neville, Strowman, Roode.
Yeah not all of these people above could have been the FOTC, but they all should have been bigger stars next to Roman in the same way Austin/Rock had Taker, Mankind, Kane, HHH, Angle, etc.
WWE's talent pool is still pretty deep, but we keep seeing the same re-hashed matches every month.
Literally none of the dudes you mentioned could have been the FOTC. And some of them, like Neville, Roode, Ryback, Rhodes, Barrett, Ziggler etc. definitely aren't upper card potential. They're mid-card at best.
And you're being disingenuous by pretending HHH or Angle were "big" stars during the Attitude Era. They weren't. The Attitude Era was near enough over when they started main eventing. Angle especially only came into his own around mid-2001 with the Invasion angle, post-Attitude and when both Austin/Rock were beginning to wind down. He was basically less of star than guys like Owens today back in 2000 where he was a comedy act for the most part. HHH only started becoming better around 2000 and his equivalent would be someone like Styles or Rollins today. These two were still far, far below Austin and Rock though. Same with Kane.
You're judging these dudes in hindsight while having the benefit of their entire career rather than actually looking at where they were during Austin and Rock's time on top. They were their bitches and mostly booked as such.
The only two guys you really have a case for are Mankind and Taker in terms of dudes feeling like stars, but even they weren't close to the levels of Austin or Rock. But they had tenure which gave them that added status at least.
Guys like Styles, Strowman, and Rollins have absolutely been booked well enough to be Reigns peers, but the problem is you have two world titles and so you have to build up two different main event cards. It doesn't help when WWE has clearly changed their booking pattern and tries to save all their big feuds for either Mania or Summerslam whereas back between 1998-2001, they were always booking big angles. The one time they actually booked against this in recent years was 2017, where they clearly did a good job of building up multiple guys like Strowman, Joe, Nakamura etc. But you still had people complaining then that they were "wasting" matches on B PPVs.