Except that neither of the things you mention affects more people than climate change will. The estimate is that there are about 54 M people World wide suffering from alzheimer.

The worst case projection for 2100 for just sea rise is 4-5m on global average (but much higher in some areas) https://iopscience.iop.org/article/10.1088/1748-9326/acb504

To put that into perspective the average altitude of Bangladesh is 9m above sea level, but the majority of the population lives in he south at about 0-1m of altitude. So there would just in Bangladesh alone be more people (let's say 50% of 160M) directly affected by climate change than alzheimer world wide. We are not even talking about the indirect effects of displacing 60M people, all the other countries and all the other effects of climate change.

Apart from that, the argument is under the false premise that we shouldnt do anything anyway because there is worse things. By that argument we should also not do something about alzheimer, because more people die of cancer.

So I question what your aim was with your argument. It was clearly using wrong facts and was under a false premise.