If things are truly this bad where the accompaniment is severely distracting, I would say something. I would give exact details as you have listed here so that your MD can figure out what the next steps should be
There’s at least one lady who sits across the aisle from me who is always video recording the Mass. A lot of parishioners video record the Mass and put parts of it up on Facebook.) is going to be a challenge for me.
I tend to lean to the side of being charitable.
Your original title asks if you should talk to the priest - I would hazard that he is aware of the situation because he was there! :D
I am genuinely surprised this is permitted!
The mistakes you noted are very normal problems for an amateur who doesn't play for the liturgy on a regular basis. While it sounds like her keyboard skills are not sufficient, I don't think an angry letter would help anything here.
Was your music director away on vacation? Does he work 51 out of 52 weeks in a year? Was he gone for a personal reason like a family funeral? One bad Sunday is not too high a price for having a good music director on a regular basis.
Try saying this, "We're glad to have you back. We really missed you!"
Also, singing loudly out of sync with both (poor) accompaniment and choir is just as distracting to those around you as the poor music in the first place.
This is why I hate parishes having only the one regular musician:
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