Can you provide any examples of this claim?
Sure. First off though, keep in mind this is a oneshot, which really ever only lays down the core concepts of a story that doesn't get expanded on unless it gets picked up for serialization. So it's not like the author has decided on all the story details, or any world building details, so everything's open ended and may not even be consistent, but I think this author did great with leaving enough mystique and providing just enough breadcrumbs where things can have double meanings, and left open ended for interpretations; nothing that locks them in to a single path if it gets picked up for serialization, since they probably haven't even decided yet.
The Smile
On P.6, "You always hide something with that smile". The mid-page panel has Joel with a forced (almost, pained) smile, where he's quick to agree with Hannah and disagree with kid Kaikashi after he specifically says "this is also your first time", suggesting he knows something (if you take it at face value, maybe he's just supporting his childhood friend, but... maybe he knows it's not her first time and it's not his first time).
On P.7 (top panel, when he exclaims that he'll defeat the demon king), P.10 (where he says "it's not pointless"), P.11 (where he talks about the repetition, and defeating the demon lord), and P.27 (where he says I'll always be by your side), he has the same forced smile of "hiding something". Every time, what he says can also be interpreted as him knowing something about the "loop" and hiding that fact, rather than just the standard hero's confident bluster.)
The confession?
P. 26 & 27 - you can take his dialogue as meaning for her to inform a new hero party she might pair with and that there's a final "confession" or another hero platitude, 'to be by her side"... or maybe he knows he'll be the next iteration, and he's telling her literally he'll always be with her, not figuratively, just like all the previous exclamations weren't just overconfident hero platitudes, but more literal. On P.15, he also tries to tell her something but she interrupts him. They both give off the vibe throughout that they're characters who suck at communicating (all those ellipses "..."), who will keep secrets from each other to protect the other while suffering themselves because they don't want the other person to know that they're suffering for the other person's sake.
Powers
We don't know what the hero's powers are. He might even be in control of the loop in some way (since on P.33 - she suggests that she has given up, and tried to escape from the endless torment but couldn't). He's the one who's adamant about repetition, even in the flashback to beat the drunk - he may have awakened a power to get x times stronger with each failed attempt back then, so that an "immeasurable difference in power" can eventually be matched by an infinite number of tries and power ups. So even if he doesn't have memory of previous iterations, he'll know what's up just from knowing his own power, and feeling the effects. He might not know she has to die in order for a new iteration to start - he might just be thinking that the cost is him dying and accumulating the pain from dying in each subsequent iteration.
There are a few other long shot possibilities that crossed my mind, but whether you think any of what I've already suggested is possible or not, I don't think hating on Hannah is justified. In an infinite number of loops, we don't know what she's tried and what she hasn't tried to get them as far as they got in this iteration. Maybe in all the iterations where she told her party everything including her power, those resulted in even worse outcomes and earlier deaths.