The premium currency thing doesn't actually have to do with some sales tactic, it's FAR less sinister from the POV of the dev and publisher: it has to do with legalities and customer experience. Purchasing a consumable means the game manufacturer isn't permanently responsible for the content they then buy with the currency of something happens to the account data. It means A LOT less upkeep and legal cost on the publishing side. It's in no way a "let's trick the user" tactic. Besides, casual gamers are usually very good with numbers compared to regular gamers. It's mostly casual gamers who plug everything into excel sheets to find optimal strategies - I did it all the time in Utopia (an early casual browser game a few of us played), and helped lead a Kingdom to the top of the game during its peak years.
Also, the prices aren't 1:1 because of discounts for higher purchases. And $1.00 for 12 premium currency is fairly simple to understand, it just means that an 80 item costs 80/12, incidentally about 6.66
(6.67 with rounding)
Some of the actual strategies strategies:
Random numbers = effectively, take a bunch of items, weigh them out by percentage, and generate a number. Advertise the best items.
Up-sells = advertisement of purchases in the game. Some games are absolutely obnoxious with these, while others integrate it very well, only surfacing them when the content launches, unlocks, or surface notifications when the content has a functional benefit.
Conversion tactics = Builder in clash of clans, to get a few extra, it is cheap, so you make a value calculation "I am going to play this game more than just a bit, here's a few dollars in a one time payment to make it a lot easier, it would be silly not to do it!" But then that gives the player a taste for spending by giving a huge amount of positive reinforcement - typically Instop with the conversion tactic payments, they're almost always well worth it in my opinion.
Limited time offers = putting on sales or limited time availability to increase impulse buys.
Premium currency rewards = yes, this works. It gets players used to spending.
Of course, engagement strategies are key. Put something in to cut down session time, and increase the painlessness in regards to accessing the gameplay features. Pokemon Go does this CRAZY good with 2-30 second sessions, and the game shifts in and out of "sleep" mode with the gyroscopic sensor - when the device points down the game did a and disables processes, then you just flip your phone up and you're in game in less than a second. People will play 10 sessions in 10 minutes. Sometimes as simple as hitting a Pokestop, and putting the device down which immediately throws it into game sleep state.
But to comment on the "pain points" one: this is typically called pinching. The reason why games don't do this anymore, unless they are already established, is because it's a failing strategy - effectively, all of the pinch payers are invested in games and won't budge, they're paying to rule their games. These games usually have a lot of low or non payers, and a few VERY big payers. Games are mostly easing these up for the players now, because DAU is what's important.
What games are doing now is trying to encourage retention of daily active users, give them an experience, and give them different ways to spend money to invest in their experience. An invested player is much more likely to remain playing. Devs want to make a game that users want to pay for, by providing value to the purchase items, but not pinching the users to buy them.
And yes, I've been a shameless fan of casual games since Utopia back in the 90s. I like short play sessions with long term goals. But that doesn't mean I don't love my insanely long strategy or RPG game sessions either, I have different needs for different days of the month.