The Plant Upgrade System is Plain Awful

In both the previous and current build of Plants vs. Zombies 3: Evolved, there is an upgrade system for the Plants, to counteract the Zombies themselves getting stronger. However, nearly EVERYTHING about it is heavily flawed. There are two main problems that need to be addressed, if the whole system itself isn't removed.

1. Lower Merge Tier Plants end up stronger than higher Merge Tier Plants. This causes players to not use the higher Merge Tier Plants, as merging them has a weaker result. For example, by default a Repeater has twice the Damage Per Second (DPS) of the Peashooter, which is its previous merge; BUT not only do you need to upgrade the Peashooter BEFORE can upgrade the Repeater, it's also more costly to get the Repeater to the same level, almost forcing the player to NOT use the Repeater. The Repeater should always be twice as effective as the Peashooter, as the Slaw-Slinger should also be twice as effective as the Cabbage-Pult. If anything, upgrading a Plant should also upgrade its potential Merges at the same time, even if they're not unlocked, with Plants that have two different prerequisite Plants require both to be upgraded to the same level.
2. Grinding to get the necessary materials to unlock Plants, and to an extent, upgrading them, is insanely slow. This is mainly thanks to the Zen Garden being the bottleneck; There are very few slots to grow Plants, harvesting them gives paltry amounts of resources, and there are so few times you can actually plant them per day! The grinding MUST be reduced. Perhaps the amount of resources from harvesting them are increased somewhat by upgrading them, as a better incentive to upgrade them other than dealing with stronger Zombies. However, this makes the first problem stand out even more than having to unlock them already does; Therefore, I believe unlocking a Base Tier Plant should also unlock all of its Tier 2 Merges, while any and all Tier 3 Merges will be unlocked much later in the game.