That’s true. But I wouldn’t be worried at all with a 1-3 year old used bikes. Bikes are generally pretty sturdy, and spare parts aren’t all that expensive. Suspension needs servicing 1 to 2 times a year, whether you buy it brand new or used.
I know that its is on the list that you posted, but I got my partner a Polygon Sisku T8. Pricing and availability were large drivers for this choice. Granted it is way too small for me to actually get a ride feel, but the build quality and component spec are really nice for the price. The experience with bikesonline was just fine. The upgrades on the fork/shock and brakes might help with the descending confidence you desire.
If you have a current bike, I would spend the whole/most $3k on a frame and switch the parts over to the new frame and upgrade those as you can afford it. A $3k full suspension bike will have low end parts anyway. That’s how I do it.