Sorry, I mean to say: there's no inherent evolution of plot or mechanics. It's a game that's literally defined by "numbers increasing on the side of the screen, and microtransactions to make those numbers go up quicker." What would that look like without the microtransactions?
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Try to think of each of them as a graph of growth over time. Gold is roughly upstream of DPS, but There are additive, multiplicative, and even quadratic effects than may be applied to that relationship in the form of hero powers, items?, etc. However, since by design the relationship between hundreds of effects (mostly in the form of hero powers) isn't clear, some purchases are easily 100,000,000,000,000% better than others, which is to say one wastes your gold.
It's more of a long term time based math puzzle than a game, but there is definitely an evolution of mechanics, as you put it. Also despite the name, I'm pretty sure you pretty much never click in it past the first 10 minutes.
MMOs have been wildly popular in the general community, precisely because there are no significantly complex mechanics. Yes, there can be, but a very small portion of the player-base are engaged at that level. You don't need amazing aim. You just press a sequence of buttons. The plot is often totally incoherent and a lot of people skip it. And plot can be supplied by the player's imagination, fitting in with existing fantasies they hold (writing fantasy dialogues for your virtual pet, or I'm the king of the realm, building it by clicking things).
Even FPSes are changing, in Blizzard's Overwatch, the most loved/despised hero Mercy[1] is "skill-less". You're not trying to get head shots or twitch aim or anything, you're keeping 5 bars full while moving around with very simple mechanics. And love it or hate it, you can't deny it's brought in a lot more diverse set of players to the game, I've never heard so many female voices in an FPS.
It make me think that games can be thought of as combinations of several elements, plot, progression, mechanics, difficulty, etc.. Some people like parts part of that. They hate other bits of it. The progression thing seems to be one that's very easy to "exploit" through gambling mechanisms, it seems to be some sort of built in congitive mechanism that probably benefited us when you needed to plan ahead to build a shelter, or go on a hunt, or go out and get X berries, or anything that required a multi-step process for future planning.
[1]Overwatch is a 6 v 6 first person shooter team game where there are lots of different characters to choose from that have very different weapons, skills, and roles, including healers. Mercy is a healer who can heal using a beam that requires extremely basic aim and can fly from player to player. This has allowed players without highly developed aim or positioning skills to enter the game and enjoy it, and then gradually develop those other skills to move to different heroes. The general consensus in the community is that this has allowed it to be much more accessible and fun for people who haven't been playing Halo/CoD/Battlefield from the age of 12.
The reason why they are easier is because you need effective tanks and healers in the game, and hard healers or tanks as the only option will make players just be DPS instead. This is why Ana always sucks and never solved the problem of adding more healers; if you like sniping, widowmaker or hanzo is better, and if you like healing, Ana is really hard to heal effectively with due to lack of defense and the need for precision much more than any other healer.
I think the Hanzo/Widow problem might be your personal view more than anything, there are lots of players who like winning games and did play Ana over them. The Hanzo/Widow "I want to DPS"[2] problem wasn't too bad until the disastrous Mercy re-balance caused a lot of problems including marginalising Ana players. Those sort of players don't like playing Mercy, so ended up as DPSers or, at best, Zenyattas.
Personally, I think the whole game would be simply better if they deleted Hanzo and Widow. I don't think snipers should be in a team-based, objective game.
[1] For the benefit of others, these characters are known as tanks (soak damage but don't deal as much) and usually initiate a full team fight, a match can be seen as a series of fights and knowing when to "push" is a key skill of Rein/Winston.
[2] A DPS is damage per second player, they do a lot of damage but are easier to kill. They can attract some players who aren't good at playing the objective and are just trying to get kills. A lot of people consider this role to be the most fun in Overwatch.
That's demonstrably not true. Universal Paperclips[1] had a progression, with new game elements becoming unlocked. Spaceplan[2] had a plot, and quite a bit of humor, and was absolutely worth paying for.
That's false. Skill is not required. It can help you progress faster, but it is definitely not required.
And I would argue that, since Clicker Heroes has exponential progression (outsiders) on top of exponential progression (ancients), that if you lack skill you're not going to get nearly as far as in any other activity, when measured in absolute terms. My max hero souls per primal boss kill is currently at e132. If you don't know how to optimize ascensions and transcensions properly you're not going to get very far at all, and will make very slow progression even at around e3. That's over one hundred orders of magnitude lower.
(Yes, the game is absurd.)