This is always the straw man A/B testing people reach for. When in reality, this only works on the worst possible designs or bizarre layouts, that no one really uses. It's a myth that you can somehow ring out extra few % by making tiny changes to fonts and colors -- in every case, they simply stop the experiment when the results tip in their favor.

The ONLY time I've ever seen it used successfully was to make changes to the layout of ads, making them look like more organic content or likely to be accidentally clicked. You can see this at work if you've ever clicked on an ad by mistake, or maybe you were trying to close the ad and noticed someone has "optimized" the close button placement using one of these A/B tools.

There it is, that's the market for these tools. That represents the vast majority of the these companies use-cases, revenue and usage. Anyone else who implies an innocent intent is either ignorant or inexperienced.