I understand the points being made by frustrated fans, but let's look at this game through a more practical perspective.
1. Pokedex: most fans are upset that there are "only" 400 Pokemon in the game, but let's think logically here. In a completely new region, is it expected to find every Pokemon from other regions in Galar? Every region should be specific to only a handful of Pokemon. Fans were a bit spoiled in the past couple of entries, where you could acquire almost any Pokemon. If you're upset that you can't catch your usual go to Pokemon, perhaps it's time to change up your strategy..
2. Leveling up too quickly: This complaint probably requires the simplest logic. I have come across many users complaining about how it is so easy to level up their Pokemon. Although the experience share candies offer new players the ability to level up their Pokemon quickly, there is a solution to those who are old school players. Ready for it? Dont use any of the experience share candies! In past titles like X Y, I would simply turn off the experience share to create more of a challenge. And the same logic could be applied here.
I am not bashing people who are complaining about the game, they have the right to do so. Instead, I am asking those who are complaining to save their energy and time, and perhaps find a solution. Is Sword and Shield the perfect Pokemon game? Far from it. But they hit a home run on many aspects of the game such as the Wild Area. In conclusion, enjoy what is presented to you and start enjoying the game for what it is!