Is Priest supposed to be fucking garbage in WoW classic?

I deal no fucking damage, i have nothing i bring to the party, my heals are low and consume too much mana let alone have long casting times.
This entire dungeon i spent our of mana just hitting enemies with staff watching allies die and trying to shield them only for shield to break non stop, it took us like a whole hour, we wiped several times and people kept leaving and rejoining

How tf is Priest so mana hungry? Even if i ignore the long casting, i heal twice and out of mana, I had to drink like 20 coldmilk drinks making my team wait for me every time