Typing MathJax takes so much time for me.
An additional selling point for MathJax over images, is that the above concern is probably short-term only, for you. The abstract ideas involved in presenting MathJax are much simpler than the abstract ideas in a generic Math course.
Over time, inevitably, you will type MathJax just as fast as you type normal English. This is because your brain will naturally start to think in MathJax, so that it becomes second nature to you. This is similar to how a person learns to type. After a while, it is as if their fingers just feel where each separate letter on the keyboard is located, so typing comes naturally.
So, one other reason that MathJax is required, is because soon it will be effortless for you.