What you say about wave is true, but the thing is, new content isn't unlocked by being reachin wave x. You get new content when you manage to accomplish objective (have 1 slime, then1 prisoner then 5 slime/drone/masked etc) Which mean that how many new wave you can hold each reset isn't that relevant to the speed at which you unlock new content. It just mean you'll have more time to try and go further in the game but that doesnt dictate the pace of the game itslef.
What wave you can clear is a direct limit on how long you have. Clear more waves = can do more between resets.
If you only have 100 seconds to do something, and that thing takes 200 seconds, making thing go 10% faster doesn't help. It just means you have to reset 10 times to succeed.
But if you can clear another wave, and that gets you 20 seconds, now you can make things go 12% faster each reset, PLUS you only need to get your time requirement down to 120 seconds. So instead of 10 resets, you need 7 resets.
The problem is that you simply don't speed up enough (disclaimer, my experience was with the 2x bug, whatever impact that has). So you're doing 10 resets to unlock the next objective which.... gives you a new objective to do. But you aren't any better at clearing waves.
Basically, you have an objective that is do ABCDE (in order).
You grind until you are able to just barely do ABCDE before you have to reset.
You unlock making E units. But E units don't provide any meaningful change to your ABCDE routine, especially because you get them at the very end of your time limit anyways.
Your new goal is make 5 E units.
Now you have to do ABCDEEEEE in order to complete the objective. Except that you still only barely have time to do ABCDE.
So there are 2 ways you can get 4 more Es. You can just sit there grinding ABCDE over and over and over, getting slightly faster each time.... Or you can increase your time (by getting to the next combat break point).
That is, there are 2 methods to progress in the game. Grind mana/construction speed, or grind battle power.
And to some extent, you're always doing both. But they're both grindy, and the steps between any noticeable change are a long time of grinding apart.
This is a porn game. A player should be able to reach the first sex scene in the first hour. Failing that is going to really decrease your audience - to the point you might as well remove the porn, and market it to everyone (not just porn game players).
I gave up before I got to see the one scene you've got in the game.