i believe that the line between drawn mockups as balsamiq was originally and some full featured like sketch is very thin, if even existing.
What makes Sketch more functional is not the sketch itself - imo Sketch alone is useless, less powerful then Balsamiq. But thanks to its plugins like those i mentioned it become even more easy and fastest tool for creating basic mockups. Plus they keep the possibility to product high-fidelity results and thanks to some other plugins their results could be converted to some other tools that helps creating full demos with transitions and animations, and with some other tools they can be even used for some sort of export to css.
Thanks to this universality Sketch become the first tool that many companies took for even for the initial sketching. And actually - if there would be an option to switch results to sketchy lines and fonts, i would switch as well. Because even the quality of the mockup is sometimes very important - you need to show it to customer very often and if you cannot e.g. change the line-height (point 4) than the results is often loathsome and client will refuse it. and the other 3 points are not about making it more real, but more - make it faster. And this is the key feature for mockup tool as i see it.
I love balsamiq for many years, you know that, but for me it feels you fall in sleep. I believe that is that because of that wrongly selected and now dead adobe air technology, that blocks your potential, but you know this for at least two years and still did not stopped to ride a dead horse.
I know that you are working on something new and i keep my fingers crossed for you. But it takes too much time and IMO you should keep trying to take portion of the Sketch segment the same way as they are slowly cutting from your segment. Their advantage is that extendibility so they are not alone who make the features and let the market itself improve their product in the way they might not even thought about and without their time and money. This is potential also for you I believe.