I have a few problems with many of the ideas in post.
"Hearthstone, the game pvz heroes tries to imitate, and I reached legend rank there".
This sounds to me like it comes from someone who's only experience in CCGs is Hearthstone. PvZ Heroes is actually one of the more uinque CCGs out there right now, with the main similarity to Hearthstone only being that it has a climbing resource value and you draw a card each turn (and this is because almost all online CCGs play like this with a few exceptions like Solforge). On the other hand it has many differences: it's lane based, it's asymetric (plants play differently than zombies), and has things like the block meter that make it a very different experience. Oh, I guess it has ranked play and quests, I guess that's why you think they are similar games (even though most CCGs use this popular system of rewards and competitive play).
"There are no premium currency there".
Yes there is, its called money. You can buy packs and entry to the arena directly with money. The only difference to here is that you have to take one extra step here to first buy gems, then buy whatever you want with those gems.
"Free means free and gems aren't free in this game."
Yes there are. It is true that there aren't an unlimited amount of gems per day in this game, but neither are there in Hearthstone. You are limited to 1 quest per day and a certain number of gold that you can grind. Ranked is just as limited and as difficult as it is here (though I definitely had a much easier time climbing this ladder than the one in Hearthstone) and the only really "unlimited" way to grind in Hearthstone is the Arena. I don't know if they will add something like that here, it would certainly be nice, and we can certainly hope but give it some time, this game is only a few months old while Hearthstone has a few years behind it.
"Ever heard of "time is money"? I've even specifically mentioned it in the OP, 40-50 gems per day is nothing since you need 2000 for the most obvious purchase. Time investment is too much for the reward you get in the end"
This is the most pathetic thing of the whole post though. Basically, you are equating playing PvZ: Heroes to having a job. "Time is money"!? Yeah, that applies when you are working or taking care of a family or something constructive but THIS IS A GAME!!! You don't play to make money, you play to have fun so basically the time you spend on this game is your freaking return on investment, not the other way around. If playing this game is a chore, then, yeah, don't play it, but don't write bullwad about Time is money!
Of course, you are free to give feedback to the developers saying that you feel that the progression is too slow for you, which is what you really meant to say, I believe. Personally, I disagree, though. I found that getting the full set of commons during the first few weeks of playing and then purchasing the 2K packs from gems obtained from the quests and ladder gave me a very decent speed of card acquisition. Perhaps your problem is that you are not getting as many of the highest rarity cards (legendaries) as in other games (Hearthstone) but then you really have to think about just how important they are. With the current metagame I can guarantee you that legendaries are by no means critical to having decks that succeed.
It also sounds to me like you are incredibly impatient and are incapable of enjoying a game for what it is. You don't need to get all the cards within the first month to have fun or be competitive, that's just not how it is supposed to work and if that's how you expect it to work then no wonder you are upset and seem to think that the game needs money to be played.
Here was my progression:
First 2-3 weeks: Got the first 6 heroes and spent $6 for the starter pack to get an extra hero. Played enough to get all the quest gems (since you can accumulate 3, you can sleep 9 hours without missing out) and got my first 2K pack. I was lucky enough to get 2 new heroes, though back then they didn't have any hero quests and you only got half the cards you get now, but that was enough to improve all my decks considerably and make it even more fun.
Next 2-3 weeks: Got up to 700gems and then got a flash sale for 1300gems so I went for it. Only got 1 hero though (and half the cards you get now).
Took a 1 month break.
Next 2-3 weeks: Got another 2k gems and this time got a whooping 3 heroes.
Final 3-4 weeks ☹️after global release) This time there were hero quests so between that and the ladder and the normal quests and the weekly 100gems quest I eventually got to about 4k. I played a bit more and eventually hit that elusive 5k gem mark and decided to go for it. Got only 1 new hero but lots and lots of cards (and planty of legendaries, about 5!)
To me this is a pretty great rate of progression. It took me about 3-4 months to get to taco league. During this time I had many, many hours of fun playing and a smooth progression. To me, that is a good thing, since, you know, I downloaded this game to spend time on it for fun, not to arbitrarily get gems.
If to you this sounds like a terrible deal to you, then that's your problem right there, you are just focusing on quantity of rewards as opposed to looking at what the fun and joy you get from the resources you have in the game.