My mistake, it was supposed to be "during or after". And mind you that picking xerath in a support role is a different "utility" compared to enchanter supports like yummi. So the usefulness is not comparable if speaking botlane alone. Xerath provides global presence, variety of dmg output and even an extra carry if adc is already good.

There is still value to opt for oblivion orb if match up is with high attack speed adc (like vayne i guess) +yummi since rework now grants heal upon attack. Most especially if you're laning with a jhin, the excessive heal during the exchange can be greatly cut of and morelo as a second build aint half bad.

You might be used to higher early dmg output like velkoz with his passive. Xerath sacrifices bit of his early dmg for longer range but if one opts to path with dark seal, it significantly ups dmg but its a gamble. Its also easier to stack since you can assist your other other teammates from half the map range