Yes, and no.
The term "overpowered" is always contextual.
Guiding Bolt is a Cleric spell, and Clerics have a problem with too often being used as dedicated healers (your mileage may vary). Heck, I created a Cleric/Wizard geared as a sort of offensive powerhouse one campaign, and the party STILL tried to bully me into being the healer- healing players not even CLOSE to going down, early in the fight... The game developers needed to make Cleric fight a bit above the power curve to give it more appeal to players.
What's more, Opportunity Cost. Clerics are critical to a party for healing characters who go down, or are close to death, so their offensive spells need to be more powerful to compensate (earlier, it's stupid and a waste of offensive potential and spells- which doesn't stop many parties from pressuring the Cleric to heal then too...)
Cleric using spells offensively instead often have a much greater cost to the party in terms of shorter time-to-live and lost damage potential from downed characters, than other classes, unless it's a healer-rich party (many players, selfishly, don't take any healing abilities). So their offensive spells need to punch a bit above their weight class to make up for a typical party's overreliance on just one, or maybe two (in larger parties) healers.
Even so, Guiding Bolt can be overpowered, if the DM overly favors "tank" enemies with very high HP and Armor Class. But with the drawbacks of Cleric running out of spells, the issues with too few other players typically taking healing roles, and its comparative weakness against very low HP or AC foes (where Advantage isn't that useful: either because a single hit from ANY spell will tend to kill foes outright, or most attacks already succeed to begin with), it is balanced for the class it is assigned to.
TLDR: If you stuck Guiding Bolt on another class, it would be overpowered. But given Cleric's typical role as party healer (and the incredible downsides of Cleric running out of spell slots and being unable to revive downed characters), as well as consequent lack of popularity (it's also often a stressful pick for players who want to be a Cleric and NOT act as party healer), Guiding Bolt is balanced for Cleric.