Actually, that is not how Scripture presents it (you are forgetting that the clay was a "lump" before it was formed into each vessel). Likewise, there is no distinction between Jacob and Esau except God's favor."at the start"..."separate from the beginning"... that's exactly how the Bible presents it:
"being not yet born, neither having done anything good or bad, that the purpose of God according to election might stand...Jacob I loved, but Esau I hated"
"Or hath not the potter a right over the clay, from the same lump to make one part a vessel unto honor, and another unto dishonor? What if God, willing to show his wrath, and to make his power known, endured with much longsuffering vessels of wrath fitted unto destruction: and that he might make known the riches of his glory upon vessels of mercy, which he afore prepared unto glory,"
The problem comes in when ideas are taken from Scripture and applied to different contexts or explanations. The conclusion may not be wrong, but there is the potential that it can be so we have to be very careful.
I agree with you, BTW, in God's purpose according to election. My concern here is the care that has to be taken so that what we end up with remains biblical (or at least does not detract from what is biblical).
Another aspect (for the Calvinists, anyway) is in a logical progression. Here the Reformed have been divided. Is election pre or post Fall (did God elect prior to the Fall or out of fallen man). How one thinks of this issue affects how one addresses the OP.