Sorry , but I believe your post proves the point against you.
1. There are approximately 100,000 transgenders in the USA.
2. US population is about 330,000,000.
3. Transgender population is therefore about 0.03, call it 0.05 for argument sake.
You state that rate of these murderers is 1.3 % of all shooters - so you are saying transgenders kill more per head count than other people.
Therefore MTG has a very valid point.