Dell is the way better deal. The 11th gen cpu will run considerably cooler than that 9700, and with stock Intel coolers, that's kinda important for audio sanity.
Dell uses a better grade of OEM psu, the XPS generally has Delta or Seasonic OEM, Lenovo is generally FSP and on the low end of the quality scale.
1660ti and 1660 Super are almost the same thing, not enough of a performance gap to worry about.
Ebay vs Dell factory warranty. No brainer there, and Dell has tech help for a year, free standard, I believe. Just be careful to read the fine print Very closely, or Dell will sell you a warranty package that's not really anything more than the standard warranty to begin with. So read everything in the sales contract, Dell likes to sneak additions in at the bottom of the page.
I think the Dell. All else being equal, the i5-11400 is a better CPU than the i7-9700 for gaming, where you don't really need 8 cores. 6 cores is even pushing it for some games. I have an XPS 8940 sitting on the desk beside me, right now, 10th gen i5 instead of 11th. I installed my own video card, a GTX 1080 Founders Edition, because the seller bought it originally just for the video card.
Dell make decent office use pc's that are made to work 'as is' right out of the box, with no regards to upgradability, repair, expansion etc. Office pc's and gaming use pc's are not the same thing. For gaming pc's, Dell is currently in a race for 'Dead Last', with just about Everything tested getting the coveted 'its Better than Dell' award in gamersnexus reviews.