if the SS benefit formula had a linear relationship between earnings and payout they wouldn't need to do WEP
but SS's goal is to take into account total career earnings (including those outside SS jobs) and scale back payments the more money you make
this is so it can treat someone who only earned 500$k total over 35 years in a private sector job differently than someone who earned 100$k a year for 35 years (30 of it in a government job and 5 in a private sector job paying SS)
Surprisingly, the reason for the existence of WEP is actually completely the opposite of what you are saying.
What a lot of people don't know about Social Security is that the benefit computation methods used are all tweaked towards favoring lower income workers. In other words, a low income worker literally gets more out of the Social Security system for each dollar of lifetime taxes paid into the system than do high income individuals. That is an absolute fact that you need to accept because it is true.
This is by design, as there is a presumption (which, fairly is mostly true) that the majority of lower income individuals will be more reliant on Social Security at retirement than would be higher income earners (who may have savings, investments, 401k, pensions, etc). The use of the "bend points" (there are three of them) within the computation to apply or remove this bias is what allows the agency to do this while using the same computation method for everybody.
Every person who works at least 10 years in jobs covered under Social Security has the possibility of becoming insured to receive benefit payments. The way the WEP law works is that it alters the bend points in the computation to remove the "bias" towards lower income workers for people who do not have 30 years of coverage under Social Security. It also applies a measure of "value" to work of recipients of noncovered pensions that isn't applied to any other class of worker in the Social Security system.
That was all background stuff. Here is why I don't agree with it.
Take your hypothetical 500k worker. He has a trophy wife, Bambi. Bambi goes to the spa and power shopping every day, and has really nice brunches with her fellow trophy wives. She does get the sporadic urge to work, but is usually doesn't last long before the urge leaves her (after all, her husband makes LOADS of money). So, she does it in spurts when getting the urge before quitting often. If she does this for 10 years or more, she could get insured for benefits. And, because she didn't work a lot, she is presumed by the design of the benefit computation to be a "low income worker" and thus receives the full effect of the inbuilt computational bias as such. Sure, she'll get spouse's benefits from her husband, but the spouse's benefits plus her own retirement would be more than what she would have gotten just as a spouse had she never worked on her own due to the way that separate computation works.
Or, look at another situation which is very common. I have relatives that are lazy. Pure and simple. They'll get a job, then when it interferes with their welfare, Medicaid, and food stamp benefits, they'll quit on the spot. Or, they'll quit or be fired because their employer had the temerity, "gasp" to force them actually show up for work on time when scheduled. When they can't pay their bills, they sponge off their 76 year old grandmother. My lazy cousins, when they work enough (and they will, as it isn't very hard to get 40 quarters of coverage under Social Security), will qualify for Social Security. And, they'll be classed as low income by the computation because they are. However, they are low income by choice and not because they didn't have opportunities like lots of other people are denied.
Now, look at the government worker with the non-covered pension. He might have worked 10 or more years under Social Security prior to getting his government job. He also might have worked a side job on weekends or at night to get those 40 quarters of coverage. He also is classed as a lower income worker by the computation when he is not. However, the WEP law treats him differently by saying his work doesn't have the same quantified worth to the Social Security system that Bambi's or my cousin's work does. Not only that, the WEP law further assigns a literal value on his work under Social Security that isn't applied to Bambi or my cousins. The law basically says that, unless he works 30 years in Social Security covered employment where he earns 25% or more of the maximum taxable Social Security base wage for that year, his benefits are subject to offset (with a partial exemption for qualifying years of coverage between 20 and 29). So, his work is literally treated as second class in comparison to the work of Bambi or my cousins.
And, while Bambi (and my cousins, whose wives don't work much because, like, its a "thing" according to one of them) will get full a full combination spouse+retirement benefit, the government worker's wife will likely get little of nothing while he is alive due to the reduced benefit amount and the associated GPO (government pension offset) law.
Say what you will, but WEP (and even worse, the GPO) are both just disguised cost cutting measures meant to penalize one very specific group of people under color of law for doing the exact same thing as other people freely are allowed to do with no penalty.
As I before stated, there is no fairness within the law. To slightly quote actor John de Lancie, "it will be most unfair" to all but the chosen few.