No, the disability tax credit is not dependent on income. Here is the eligibility criteria. The criteria is pretty strict so it's good to have a doctor that's willing to help explain things better for them. Remember they don't care about the criteria VAC uses for disability.
https://www.canada.ca/en/revenue-agency/services/tax/individuals/segments/tax-credits-deductions-persons-disabilities/information-medical-practitioners/eligibility-criteria-disability-tax-credit.html
I could be wrong on the 2 year reassessment as I was DEC before the PFL system and in some cases they know there's no point. In the past I've heard of some going through it and others never being asked. With how backlogged everything is I don't see VAC making any reassessments a priority if they exist.