He’s right about one thing: go for the keyword phrase that you want. But that doesn’t mean you can’t go after longtail keyword phrases while you’re working on your desired phrase.
Without knowing which SEO you’re talking about, it’s hard to say whether or not you should hire him. Some SEO’s are very good. But if you take the time to learn how to do it yourself, you’ll have more fun and probably do a better job in the long run than any consultant you hire.