I wouldn't say it's always wise to go for the top of the line. Indeed, in the past, one could often get an upper-midrange or lower-high-end part at such a discount from the top models that buying a new one after a year or two would leave you with more money a much faster card, and a good backup.
However, the current market is very different, with price inflation being more flat than progressive or proportional. Top-end parts are 'only' 50% over MSRP right now, but mid-range parts are still double or more MSRP. This skews the value, as in performance per dollar, toward the higher end. It's a ridiculous situation.
Right now, the best bang for the buck AMD card is 6900 XT. On the NVIDIA side it's the 3080 Ti. You can certainly spend much less, but in many cases, you'll lose performance faster than you shed price.
Would an RTX 3080ti have been just as good?
By and large, yes.
Where will my RTX 3090 excel?
Relative to the 3080 Ti? In those very few areas where 12GiB of VRAM is insufficient.
