The Lich King has about zero power without Frostmourne and the Helm of Domination. The Helm merely granted him dominion over the Scourge, which even that could be taken by a strong enough foe (Archimonde, for one) or interrupted by a strong enough blow (the Forsaken and Death Knight's were freed this way). Frostmourne is where pretty much all of his frost and shadow magic originated.
So really, it boils down to Frostmourne versus our artifacts. Frostmourne, as we know, is equal to Shadowmourne. This is strict lore; Shadowmourne was crafted to be Frostmourne's equal, and it was. It feasted upon thousands of souls, was imbued with the powers of blood, frost, and unholy. It was crafted from a weapon of pure light adorned with fragments of the Frozen Throne. Mere fragments of souls could manifest for devastating damage through Shadowmourne.
Now, would you argue that our current artifacts after being empowered at our forges and imbued at the Netherlight Crucible aren't stronger than Shadowmourne? The reality is that pretty much all player artifacts are at or above Frostmourne's level of power, and Frostmourne's power is the Lich King's power. That's why it was such a big deal when we discovered he left it unguarded in the Halls of Reflection.
Did I mention we also have these sick pieces of legendary armor now? Let me tell you, 1v1ing the Lich King with my artifact and Prydaz... I don't know that I'd need the second legendary lorewise. Prydaz OP.
TLDR: 1v1ing the Lich King lorewise isn't only NOT suicide, it would be quite doable at our Legion power levels.