The shot was behind left shoulder
That shot wasn't just "behind left shoulder," but too far behind it and high enough to cause temporary loss of CNS functionality but not high enough to crush the spine and sever it. How do I know? Because you already told me so, when you wrote:
I knocked the deer down but lost him
Call me "Captain Obvious" but, this much is true: YOU failed the cartridge when YOU "knocked the deer down but lost him." That's all the empirical evidence you needed in order to figure out where the real fault is found, and it isn't found in your cartridge choice. Had you put the bullet where it SHOULD HAVE gone, instead of where it went, you wouldn't be telling this blame-shifting tale of coyote-bait making woe on an Internet forum.
I’m good out to 500+. This season my shot was 335. No suppressor or break
No, you're not. I'm not, either. I get reminded of how much I suck at "500+" every time I fire a 600 yard slow-fire prone stage in CMP "service rifle" matches. If you were actually "good out to 500+," you wouldn't have rendered a mule deer into coyote bait.
I just didn’t find the creedmoor to have the killing power necessary.
You don't have enough experience with the 6.5 Creedmoor, based on a sample size of one poorly placed shot, to formulate that opinion on the basis of logic and objective reality. I've tagged 20 elk in my lifetime. I tagged 9 of them with a Marlin 336 in .30-30 Winchester. 8 of them were shot with a 170 grain Speer Hot Core handload averaging 2,150 fps at the muzzle. As you'll be tempted to ask why in the hell anyone would use a "saddle gun" as an elk rifle, I'll answer by saying that I had the saddle and the horse to go with it, and admit that hunting on a horse is cheating; you can ride right up to bedded game you might not get so close to on your own two feet, and you can see that game from your tall in the saddle position, when you might not be able to when walking. As a result, my shots were close. But my 20th elk got tagged on the longest shot I ever made on one; a 178 yard poke through the heart with a 160 grain Hornady FTX launched at 2,352 fps. I once tagged an elk while not expecting to see one and toting a Ruger M-77 RL Ultralight in .250-3000 Savage. In addition to that elk, I tagged 2 caribou with it, 3 pronghorn, 21 mule deer or more, and God only knows how many feral hogs. My handload launched a 100 grain Nosler Partition at 2,620 for less than 1,600 ft/lbs at the muzzle. To put this in even greater perspective, a .250 Savage generates recoil on a par with a 5.56 NATO and the terminal ballistics of my .250 Savage load and the 5.56 NATO loads I use now are so substantively the same that no animal would notice the difference. During the 2024 season, I tagged a mule deer at 261 yards with a 70 grain Hornady CX. I shot that deer through the heart. The bullet made an exit hole larger than a guarter-dollar coin. I went to the same area last season and tagged another mule deer at 268 yards with a 77 grain Sierra TMK, and that made an exit hole about 2.25" in diameter.
You might not believe that a 6.5 Creedmoor has the "killing power necessary" but nobody in their right mind would argue that it has LESS killing power than Hornady LeveRevolution .30-30, any 100 grain .250 Savage load, or the game loads I use in 5.56 NATO. In my hands, and the hands of others besides me, myself, and I, those loads are "amply sufficient" for killing the biggest mule deer God made.
But a 6.5 Creedmoor doesn't have enough killing power? That's delusional.
I’m trying to decide whether to go back to my 30-06. I’m also researching 7mm prc so I can use it for deer and elk
That would be applying an ineffective solution to the wrong problem. You didn't have a cartridge problem, so changing the cartridge to something else can't solve it. In the 6.5 Creedmoor, you have the same terminal ballistic performance as a 6.5 x 55 Mauser has, a cartridge that generations of Scandinavians have used to render moose into meat, but you still insist on blame-shifting your rendering of a mule deer into coyote bait on a cartridge that would have killed your animal stone-cold dead if you would have put the bullet where it was SUPPOSED to go, instead of where it actually went.
I'd also like to know why neither you or your guide seemed to pre-plan what you'd do if your animal got back on its feet again.
As a former licensed and bonded hunting and fishing guide in the State of California (#2725), I'm less impressed with your guide than I am with your blame-shifting. His job isn't done when he puts you in a position where you think you can shoot. He is supposed to anticipate what is likely to happen if you muff the shot. I suspect that you two got along famously, though, because he sounds like a blame-shifter, too. When a licensed guide and a client are out hunting together, it isn't the CLITENT who loses a game animal if a wounded animal isn't recovered, and it for damn sure isn't the cartridge's fault, either, when the onus of responsibility for turning a mule deer into buzzard fodder is on him as the supposed expert on the basis of competent legal authority.