That's just not true. Saturn V had a paylod of 43,500kg to TLI. Only the largest configuration of SLS(Block 2) exceeds that with 46000kg. A Falcon Heavy is far below that.
My point stands though: no Artemis mission has plans to launch a full Apollo style capsule + lander stack. Artemis HLS, SpaceX and Blue Origin versions both, flies entirely on its own. So what's required of both SLS and any would-be SLS replacement is a far less demanding mission than what Saturn V has done in the past.
Which calls into question: what SLS is even for? Does it add value to the mission, or is the mission subtracted from to justify adding SLS to it?