You did not say how old your grandchildren are, and to me that makes all the world of difference.
Wonky handmade gifts are fine if they are made and given by children at kindergarten. They are developing hand-eye co-ordination and having fun making things.
If, however, 10 - 11 year old children are still giving wonky handmade gifts, I agree with you that these are annoying. By age 10 they should be able to make something that looks good and does whatever it is supposed to. If they are still drawing houses with smoke blowing each way out of the chimneys or people with four fingers and no nose, some teacher is slipping up badly.
Older children need to to be taught the value of money - buying presents is one way of learning this.
Yes, it is money their parents have earned, but whether they gave it to the children, or the children earned it washing up, or mowing the lawn, is not my concern when I receive a gift that a child spent time shopping for and paid for with her pocket money.
And yes, just because they are our grand-children or great-grand-children does not mean we can't wish for something specific for Christmas or birthdays.
So no, I do not think you are being unreasonable unless we are talking about two year olds.