@newacct I think you're confusing or misunderstanding several things. If OP marries a GC holder, they would become an immediate relative. Immediate relatives include spouses, children, adopted children, and step-children. Non immediate relatives include parents, step-parents, unmarried siblings under 21, and unmarried half-siblings under 21. Citizens and GC holders can sponsor immediate relatives under the same rules. GC holders CANNOT sponsor non-immediate relatives.
I have first-hand experience with this. I have a relative who came to the US on a tourist visa. She overstayed for many years. Eventually she married a Permanent Resident, and she was able to adjust status without having to leave the country. By contrast, I have a friend who came to the US without inspection. He was here for many years before marrying a US citizen. When adjusting, he had to go back to his home country to apply for the waiver and avoid the 10-year ban. It took a little over a year, but he was eventually able to come back and get his green card. The main point here is not so much unlawful presence but
how you first entered the US - with or without inspection (legally or illegally).
A waiver is not for a ban. A waiver is for inadmissibility grounds when adjusting to Permanent Resident status. If you click on the link I posted on my earlier post, you can verify this. A ban is something that gets triggered when you become inadmissible, you leave, and you don't qualify for one of the waivers or there is no waiver for your offense to be able to return.
@Fin also makes a good point that waivers are slightly different depending on HOW you're adjusting. All of this so far is only as it relates to marriage -based green cards, because OP is talking of going that route. And I do agree with you that we need more information from OP on how they entered the US and whether they have accrued any unlawful presence or not. IF they wish to disclose that information.