Trixie actually has a lot of talent. She's just more interested in showing off than in improving her talent. It's canon that she's Twilight's intellectual equal (a genius). If she spend enough time training her magic instead of showing off, she'd last longer in a duel under with nothing but own ability. She'll never equal Twilight in magic but that's because Twilight is magic personified and thus has no real equal aside from Cadence, Celestia and Luna but she would rather difficult to beat in a duel if she actually spent time training because she doesn't need to out magic Twilight to beat her, she just has to outsmart her by using her intellect and Twilight's own magic against her. She's talented, she's just too caught up in her own ego to truly tap into that talent.