I know I'm not terribly experienced, but it looks like your main problem is that you have far too many high-cost cards. Gargologist is the only card you have to reduce cost, and will be a very tempting target as soon as it hits the table. Having a few Flag Zombies may help bring costs down even more, as well as making your Gargologists and Swimmers cheaper!
Also, having some more low-cost plant removal tricks may be useful, too. Getting a gargantuar out on turn 3 may be exciting and fun, but it would probably be more realistic to shoot for stalling a few turns and then overwhelming with a constant stream of heavy-hitters.
Escape through Time is also Hearty, isn't it? Those could help keep your Gargologists out early, and can still be very useful late-game, too! It also allows you to conjure a card, and having more options is always good!