SImple make it just like today.
How do you make it "just like today" without the events preceding today? Today has a memory, which is part of what it is. If you change the events preceding today, you change the things that exist today as effects of those preceding things--the memories, and also the physical effects. If I change the hard, painful workout I did yesterday to build my muscles, I cannot make today "just like today" because I don't have the stimulated muscle growth I earned by pain yesterday, and the relief and satisfaction gained from that. (Unless you have those memories and feelings placed at creation-time; which to my perspective is effectively the same as having had those things happen; and therefore there's no reduction in anything; it's effectively exactly the same thing.)
It is if you say that because of that it is impossible to have a universe with less pain, and still have our pleasure. They are not directly related. As in 1 to 1 for any "unit" you want ot come up with.
Okay, now you're the one making assertions without any support. I made a big list of why they appear to be related and balance each other out, including by definition (to which you just say "I disagree" with no real supporting reasoning, examples or argumentation). You're free to hold this view without supporting it, obviously, but I'm going to have a hard time maintaining patience with you if you continue to accuse me (inappropriately) of unfounded assertions while you try to get away with precisely that.
Even though you are not, I'm curious if you might have a point so I'll try to analyze that connection between want and pleasure a little more. When you want something small, and get it, you have a small amount of joy. When you want something large, and get it, you have a large amount of joy. ("Want" here can refer to the desire to acquire something or to the desire to end something causing pain--in my mind they are effectively equivalents anyway). If you are pained a small amount, you receive a small amount of pleasure when that pain goes away vs. the relief you'd experience from a large amount of pain. If you are very hungry, you receive a large amount of pleasure when you eat vs. when you are only a little bit hungry. I admit this is more of a thought exercise than a scientific survey, but I can't think of any scenario where there's not a linear correlation between the negative and the positive. If you can show an exception that would be enlightening here.
Or on the other hand because of your mention of "units" maybe you're just saying that the correlation is a general trend but not precise. That's fine to assert, but I'd really like to see some examples that support that. In a way though, from the perspective of "generating a reality" I don't know how precise you need to be; if this is a widely-recognizeable general trend, then at the entire-universe scale one would expect it to hold true even if on some small scale in some specific circumstance it may be found to be less reliable.