It actually looks quite nice. Does it allow for further html edition? If so, is the html output semantic? While most editors' html is gibberish, so is the interface, so maybe Weebly also got this right
Weebly's markup is good- especially compared to most website builders markup with poor markup (as you pointed out). Wix probably has some of the worst markup among website builders.
For reference, here's an example Wix website: http://s99433.wix.com/stevebenjamins and here's an example Weebly website: http://weeblyreviewed.weebly.com/. You can check out the markup using your console.