Instead of giving trans people estrogen if they're men and testosterone if they're women, why not...?

That would make it worse! Transgenderism isn't caused by a deficiency in sex hormones at a given time - it's caused by a deviation of a person's neurological framework away from their genetic, and biological, sex. In other words, transgenders are trans because they actually have a brain that more resembles that of the opposite sex, and pumping a twentysomething with hormones isn't going to do jack to brain structure. Meanwhile, having secondary sex characteristics (that they already don't like) exaggerated might push a transgender person over the edge into suicide.

1) Female bodied people need no more estrogen.

2) Male bodies people need no more testosterone.

3) Hormone treatment is so trans people can get rid of what gender dysphoria they may be experiencing and to help them become as cisgendered, or comfortable in their own bodies, as possible.

4) It's asinine to do #1 or #2 for people whose brains are physically and chemically the sex opposite of their body's sex. It won't "solve" anything and would likely result in immediate suicide from the transgendered person were it to ever transpire.

That wouldn't work at all, it wouldn't make them feel more comfortable as their physical sex, it would just cause a lot of problems. You should respect people's gender identities, it's not something you can just change.

That would not solve anything. Hormones change the persons body to reflect the gender they feel on the inside. They would not make the person feel any different about their gender.

No it would make our condition worse as our brains determine our gender not our bodies...