I wanted to clarify something here, because it seems to me like you are using SEF and SEO as the same things, and they are not. SEF = Search engine friendly URL's, which is a small fraction of SEO which is Search Engine Optimization. Joomla only has relevance to "On Page SEO" and no relationship to SEO, as a majority of SEO is "Off Page SEO". The two have no relationship to the other.
My Joomla and SEO experience is proven, if you visit my profile and click exams and skills you'll see I am certified in both, and among the top 4% of all 9,000,000+ freelancers when it comes to SEO.
Also you would not want someone constantly "managing" SEF urls, once you have a url for a link on your page, you want it to stay the same, if it changes all the rank that page had is lost. For off page seo you need Link building, social signals (Facebook likes, tweets, etc), and other things, in which you hire an SEO company to do.