The Material Design Team at Google have been releasing a new version of its specification last year focusing on themability. You should be able to make Material-UI matches your brand. We have some demos: https://material-ui.com/premium-themes/.
they indicate that they are showing approximately 38% fewer visitors than what we are sending across.
This number doesn’t look that bad. May be part of the answer is in: Ad blocking user penetration rate in 2017: 27.5% + people leaving the page before Google Analytics actually loads.