Well, he was already clearly "the phantom menace" all through the prequels, but yeah, it certainly adds another layer of significance to it.
I do really love the idea of his return here. Not only in a practical sense in that it's the most elegant way of tying the three trilogies together without getting bogged down in too much minor lore from the books and cartoons that 90% of viewers won't know, but also it's perfect with how George always talked about Sheev as literally "the devil". He's pure evil, the GFFA satan analogue.
Of course he's gonna be back.
To me it doesn't cheapen Anakin's arc at all, the redemption there was Anakin turning back and balancing his soul to save the next generation, killing Palpatine wasn't the important factor there. Just the means.
Still thinking he did physically kill him though. It's just that, as we know, that's not necessarily the end for someone that potent in the ways of the Force.