To say that alicorns are powerful is like saying the sun is a little warm, the sea is a little salty, and hard vacuum is short on breathable material. Twenty-seven beings that the Equestrian ponies revere in various degrees of worship from “the very hoof beats of Faust on the universe” to “very powerful beings that you should respect for that power.” The weakest can kill starships in orbit, the strongest and eldest among them are basically “do not attack, unless you want to prove there is life after death by direct examination.” They are capable of many things…
…but, some things are beyond them. They cannot bless. They cannot bring back the dead (the truly dead, not someone that died but has a cortical stack). They cannot heal beyond what is available by technology. And, the process of becoming an alicorn, Ascention, is something that an alicorn can only provide guidance once the pony has made it half-way there. Whatever counts as half-way for that particular pony.
But, this doesn’t stop ponies from trying to pray. To beg for a miracle. To ask for a blessing. To pour faith into twenty-seven being that for the most part…can only do what they can do and not much else.
For at least six hundred years, the alicorns of Equestria have been trying to reduce the size of the pedestals that they have been put on by ponies. So far…there hasn’t been too much reduction.