Oh, I LOVE this point, because I was just noting to my partner the other day that one of the many influences on Arcane is clearly Lord of the Rings and one of the places you see it most is in the way people look at Hexgems and Hextech items for the first time.
It's not just Powder who gets the glint in her eyes the first time she sees a Hextech gemstone.
The first time Vi picks up the Atlas Gauntlets, she gets the blue glint in her eyes as if it hypnotizes her. Later, Cait notes how Vi seems to believe Jayce's gauntlets will solve everything for her, to perhaps a worrying degree.
Jayce is unwilling to put down his Hextech hammer in the Anomaly future to the point where dragging it around is actively endangering his chance of survival AND permanently maims him.
Even Heimerdinger gets the glint in his eyes the first time he sees the Hextech gemstones, it's this very particular blue shine, and if I was less lazy, I'd go hunting down all the gifs and images but SUFFICE TO SAY, every single time a characters sees Hextech up close for the first time, they get a very particular glow in their eyes.
Personally, I think the metaphor here is simply: power.
Hextech gives you the power to do the thing you want to do. I'd argue the sense of power the gemstone gives Powder is what eggs her on to make her monkey bomb in the first place that brings such destruction to everyone she loves in 1.03.
Viktor becomes obsessed with the Hexcore to the point where he's ignoring the living people in his life who want to spend time with him while he's alive, like Sky and Jayce, so even if Viktor manages to stay alive he's demonstrated that he's not living.
As noted, Vi becomes reliant on the gauntlets, Jayce's mother notes with fear how obsessed Jayce has become with magic and Hextech (arguably, he's Patient Zero in all this) to the point where he's ready to die if he can't have Hextech in his life, it's so beautiful he can't imagine wanting to live in a world without it, and arguably his moment of demonstrated growth and healing at the end of the show is when Viktor and human connection replaces the value he once put on Hextech as the center of his life.
Heimerdinger also makes an interesting note when he says he thought the danger of magic came from humanity's, "Turbulent relationship with power." Which is very in line with the One Ring.
However, he goes on to say that the Arcane itself might be responsible in part for the destruction that springs forth from its use, which implies a will beyond that of the mage wielding it.
So I think on one level, Hextech and its intoxicating influence works as a simple and beautiful metaphor for power, exactly the way the One Ring does.
But, because we're in a fantasy world too, there is a deeper implication with both Hextech and the One Ring that arguably inspired it that there is a will at work, and it's a will that is seductive and a will that bends towards destruction.
From the moment people get that shine of Hextech in their eyes, they begin to act differently unless they wrench themselves from its influence. Already unbalanced people, like Powder, fall very quickly and spiral into destructive uses from it almost from the start. Stronger personalities disavow it, like Cait saying that Hextech will keep us alive but it won't save us, only for her to fall prey to its siren call after the attack on the Memorial unbalances her emotions further as well.
The lure of power is particuarly appealing to those who feel they've lost control but there is a sense that Hextech and magic by extension also preys upon those who are attracted to it.
And with the Hexcore representing the Apex form of Hextech, well, let's just say I'm not sure Viktor stood a chance at all, with how much he felt out of control of his own life (for very understandable reasons) and how it took a reaffirmation of connection with others to restabilize him and make him see the damage this pursuit of power had caused.