OP I don't think you are being unreasonable.
I'm not well at the moment, I'm struggling to concentrate to get my words out right.
But to me telling you that should feel lucky or be grateful for your mother when she knows you have had years of struggles, a childhood that was badly affected by your mother, and times of no contact etc, is wrong.
It's coming across to me as victim blaming in a way, like saying you haven't tried hard enough to make your relationship with your mother work, or you should be kinder because then your mother might be nicer, even as your mother puts you through hell.
Sometimes nothing you do is good enough, and sometimes all you can do is distance yourself or walk away entirely to protect yourself. If you have that kind of relationship, there is no lucky, there is no cherish.
And as a PP has said, even following a loss of a bad parent, the nature of the difficult relationship can leave you feeling worse rather than better. Comments like "you only have one mother so cherish her" do not help with those kind of feelings in a dysfunctional relationship which is not your fault.
You were the child in this relationship, your mother set the tone of it before you were old enough to have a chance to know any differently. I'm not saying she could help that any more than you could if she had mental health issues, but she was the adult and you were the child, so you were entirely blameless regardless of how much she could or could not help what went on.
And by the time you are an adult, the relationship is so deeply ingrained that you still wouldn't be able to change anything, especially if her issues are still ongoing and still making her a difficult person to be with.
DH's parents were very emotionally manipulative and controlling, even when he was a very young child. As a result they can still reduce him to little boy status just by ringing his phone or sending a message. He doesn't even have to speak to them, just knowing they are at the other end of the call is enough to do the damage. He was frequently told that saying no to his mother would mean he was responsible for her having a breakdown and everyone would blame him.
His mother has been in touch today, basically ordering him to send her "a lovely text message tomorrow" because she wants one to keep and show everybody. She's told him exactly what she wants him to say in this message, singing her praises as a fantastic mum 
In 2007 we lost two babies. Our first was stillborn, shortly before Mother's day. MIL had lost her mother the previous year and this was her first Mother's day without her. The whole family was told that the day must not be acknowledged in any way as MIL would find it too upsetting.
That was fine by us. We were grieving for our baby, who we buried four days before Mothers day.
On the day, FIL rang absolutely raging at DH because he hadn't sent his mother a card. MIL was apparently sobbing uncontrollably because none of her four children loved her anymore. DH pointed out MIL's request not to do anything to mark the day and FIL said she had changed her mind and we should have known how important it was to MIL to get cards and presents. DH pointed out it was my first Mother's day without our baby, when it should have been enjoying it as our first as new parents. We were told that they had forgotten all about that, but it wasn't the same, and that we had ruined MIL's day.
They seem to forget they ruined our son's funeral, throwing a tantrum because DH sounded miserable on the phone when MIL rang him the night before. I'm not sure how they expected him to sound the night before he buried his child.
You don't cherish this kind of person, or count yourself lucky that you have them in your life.