I'm a second wife so I'll admit my bias upfront. That said, I will preface what I'm about to say by quoting myself from the other second wife/stepmother thread.
I think that people are conflating divorce and death into one marital situation. When you get divorced in a community property state (no prenup) the judge divides community property down the middle because during the marriage it's assumed that both spouses have access to 100% of marital property. If a spouse dies without a will, the principle of "Survivorship Marital Property" kicks in and 100% of community property goes to the surviving spouse because again, the assumption is that both spouses have access to 100% of marital property. Marital law addresses the spouses and nonadopted children from a prior marriage are not factored into the community property equation. Separate property is treated differently.
If we are talking regular people money, i.e., an average price house for the area lived in, emergency fund savings, retirement savings, life insurance that pays off the house and covers funeral expenses with a lil something to help the surviving spouse live on then the second wife should inherit 80-100% especially if she got significant time invested in the marriage and they weren't trying to leave each other. The deceased leaving momento's and breaking of some change to the children of the first marriage or situationship is fine. Again, I'm talking regular people money because even though everybody swear they go die a millionaire
Half of Americans die with almost no money
If we are talking life changing money, the table is open for negotiation. There's times when it makes sense for the surviving second (or tenth) wife to settle for 20% vs 50% vs 80%.