@saintlydevilis Let me give you a small example. Let's say you are a boxer, and you are facing someone who is twice as big as you. What are you going to do? Try to knock him out by brute force?
-Is it possible? Yes, yes it is.
-Is it going to be hard? You can bet on it.
All sides and classes have their advantages and disadvantages. If you try, for example, to beat an armored zombie (like an All-Star Zombie) with a couple of small plants (Like Shrooms or beans), well... you are going to have a bad time. Same thing happens here.
Zombies are the big guy. They are strong and hit hard. If you play close attention to them, you'll see that they are meant to be the aggressors. Zookeeper, Aerobics Instructor, Overshoot, Frenzy, Armored... etc. You CAN beat them by brute force, but that's exactly what they wan't you to do because they are good at it.
Plants are the small guy. They can hit hard, of course, but most importantly they are smart. They know they have a natural disadvantage against the zombies (it is the lack of feet if you were wondering :P), so they have a lot of ways to "sneak" damage past the zombies, and directly into the Zombie Hero. Mirror-Nut, Astro-Shroom, Grapes of Wrath, Sportacus, Admiral Navy Bean, Attacks next door, Strikethrough, Bounces, Transformations, Insta-kills (Briar Rose, Winter Squash, Chompers) etc, are ways that they can deal with these big guys and affect the enemy hero directly.
This is all speculation and theories, but maybe you are not using your resources efficiently.
The best advice I can give you is:
Can you kill it? - If yes, do it. It will prevent the enemy Heroe from buffing it.
........................- If no, ignore it. Focus your power in another lane.
But... be certain that you CAN indeed kill it. Even if the Zombie player saves 1 brain for the Trick Phase, consider that he may be baiting you into a disadvantageous position, waiting behind the other screen with a malevolent smile for the moment the can say... "FOOL!! YOU JUST ACTIVATED MY TRAP CARD!! (Shrinking Ray / Escape Through Time / Rolling Stone / Barrel of Barrels / Acid Rain / Cut down to Size / etc)"
Remember: Work smarter, not harder.