I respect what you've both said as good practices. The fact is though that not all of Exact's lawns are going to have the same lab results, nevermind that none of us can test every lawn every year. In addition to the suggestions you've made, I suggest considering several other factors - beginning with what are the available products or combinations of products available in your area. I know that is a little backwards but short of custom blending it needs to be considered.
Other considerations include: what is known about the history of the lawn, underlying soil type, amount of precipitation or other water compared to other years, is K being mined out of the yard by bagging clippings, is the lawn being mowed properly and frequently enough (minimal self-inflected injuries), amount of shade, dsirable species present, will the fertilizer under consideration contribute to (or help) any pH problem the lawn has, if any.
On my invoices I have a section about what to expect and another for what needs to be done next. Obviously then I believe it is important to keep what is next in mind while I am doing what is today. And customer expectations: what do they want and expect and what have you promised them
In response to the original question, I dearly miss having a season long target of 4:1:2 here. I can't prove why and I can't swear things are any worse, but the advice we were given at MSU is soils classes was to start with 4:1:2 or 4:1:3 and adjust. We are too close to when we lost P to now yet what difference, if any, it has made in turf.
I can be more flexible than people who do lawns. All mine get tested usually before I start the first year and at 2-3 year intervals thereafter. P and K levels rarely come back as needing attention or a change for me. Micros and pH are occasional issues. Soil texture and OM (separate test) sometimes need attention. Almost everyone here sees more different customers in a day than I see In an entire season. None of my places are on the same program although many have similar goals.