It's entirely normal and justified to think this. You're not allowed to say it out loud but don't worry tons of us are thinking it.
My elderly mum (abusive, personality disorder, bully, controlling etc) has been 'dying' for about 5 years. She must be costing the NHS absolutely thousands a week to keep her alive (she is on about 30 tablets a day mainly heart related). She has carers 4 times a day to wash/dress her and give her tablets and microwave a dinner. Everything else falls to me plus a friend. We do housework, admin, house maintenance, washing, take her to appointments and deal with the constant phone calls about her.
She's been in hospital 4 or 5 times this year so far.
Everytime some phones me from the hospital or social or doctors or emergency alarm pendant people I think to myself 'please god let her be dead' but nope she's fallen agin, or had bad chest pain, or got lost but still here.
It's getting harder and harder to pretend to the everyone that I give a shit because I honestly don't.
I wish she would just fuck off and die.
Even if I didn't feel like this about her what on earth is the point is keeping a person alive when they are confused, housebound, can't microwave a dinner themselves, incontinent, can't work their tv, can answer the phone.
We are currently organising a carehome for her and honestly I hope the shock of the move kills her. They say the stress of moving for frail elderly often does finish them off.
Nobody understands until they are in this position.
You are not alone.