The short answer is, no. Simulations in PokeBattler for both Extrasensory/Psychic Exeggcutor and Legacy Confusion/Psychic Exeggcutor place it just slightly above Gardevoir in terms of TDO and in terms of DPS, against both Counter/Close Combat and Counter/Dynamic Punch (Assuming all Pokemon are Perfect IV, level 40).
However, I noticed that Exeggcutor had slightly more deaths than Gardevoir in some of the simulations, especially those in which it ran with Confusion when Gardevoir ran with Shadow Ball.
If you want my takeaway on it, Shadow Ball Gardevoir is actually the better investment of the two despite slightly trailing in performance in most cases behind Psychic Exeggcutor against Machamp. It's better for defending gyms and useful in more matchups (such as Focus Blast Alakazam/Mewtwo/Gengar), whereas Exeggcutor running Psychic really is outperformed in DPS by many other 'mons, notably nonlegendaries Espeon, Alakazam, and Gardevoir, and legendary Mewtwo and Latios, and outperformed in bulk by nonlegendary Metagross, and by legendary Mew, Lugia, Latios, Latias, and Mewtwo.
If you want a non-DG Gardevoir to get ahead of Exeggcutor, Psychic edges out Exeggcutor with Psychic as well. However, even with Shadow Ball I would use it over Exeggcutor unless you find yourself timing out and happen to have a better Exeggcutor handy.