300WINMAG has been my goto caliber for decades. When I first obtained a 700Rem in 300WINMAG, I used 168gr bullets and looked for as much velocity as I could get. That was about 1985. I killed lots of stuff with it, didn't dial for elevation and just guesstimated distance and elevation. I could shoot it about 5 times before I didn't really want to feel the punch again.
Then, about 15 years ago, I started realizing (I know, a little slow to the "game" but better late than never) that Ballistic Coefficient was a serious factor and started looking for that number as close to 1.0 as I could get. I figured out at some point, maybe about 2010, that a 210 Berger leaving the barrel at 2950 fps would be flying faster at around 400 yards than that 168 gr bullet leaving the barrel at 3200 fps.
Then I got interested in ranges farther away than 500 yards.
I installed a muzzle brake. Then I had that old action blueprinted and installed in a McMillan stock with a Brux barrel and a good trigger and that was the start of spending many thousands of dollars.
That original action, I still have in that McMillan stock and still that same barrel but only around 700 rounds down it. I have a shot book but just going off memory. It is pretty heavy, plus the brake, I have fired it in fairly rapid succession 100 times and had no problems with the recoil.
I've never fired a 6.5 Whatever and will not try to say that it is inferior in any manner. I do have smaller calibers...7mm Rem Mag, 280 Ackley, .308, 5.56...
If I have need, or want, to shoot at something that is a long ways away, I'll use one of my 300WINMAGS.
Caveat: I have a new 30Nosler that I have a load developed for, very accurate at 100 and 200 yards but have not yet built dope for any other distance. It will replace my 300WINMAG stuff and I intend to sell all of my 300WINMAG stuff. Also, I have a 338NormaMagImproved in the works for just for heckuvit.
No...the 300WINMAG is, by no means, obsolete. It will still be relevant when your grandchildren are grandparents.