I would suggest to add more items that can be combined with saradomin artefact. Because how it is now it just feels like saradomin artefact is less useful. If we compare it to the other artefacts we see that they can all be used to upgrade some armor parts, but for saradomin there is no armor you can upgrade. so in order to make saradomin artefact more useful I would propose to add the possibility to upgrade staff of light (sol). This would make the saradomin artefact more useful and would encourage more players to kill saradomin hardmode.

I would give the upgraded sol better stats but not better stats than demon wand. Because that would make the price of demon wand drop and it would no like be rewarding enough to kill Yk'lagor. But i wold make the stats good enough so that upgraded sol is a good alternative for the demon wand. the better stats of the demon wand will be compensated with rune saving ability that sol has.

I totally agree with the idea,
it will make SOL more useful.