Many people assume many things.. Some true, some false...
It's your choice to listen to another. There are many so called, "seo experts" talking crap in webmaster forums, sharing their junk making newbies believe it.
URLs aren't a major factor. Stick to writing interesting content for your search engine visitors,
Once your URLs aren't too long, there isn't any unnecessary words/numbers and they're easy to understand, then it's "search engine friendly".