The issue is not that the cheap tripods don't last long or have limited functionality (that is expected), they simply do not work full stop. Frame your scene and tighten the head with any lens like the 70-400 and the head will collapse under the weight and point downwards several degrees from your framed position, ruining your composition. With skill you can try to compensate by framing above your intended final composition and let the slack in the head slide the frame back into the correct view. I found with these cheap nasty tripods that leaving the head locked as tightly as you can and simply using the legs to change the framing is the easiest method, you have to do it by trial and error because you can't look through the viewfinder while you are doing this.
Then when you take the photo you find soft blurred images because at 400mm on a crop body the finest vibrations become highly visible. Exposure delay and a remote become critical rather than just a good idea, god help you if there is so much as a breeze or pigeon farts 2 miles away. You can try to improve things by using your 4 piece legs as 3 piece legs so your 3kg of camera gear is not supported by the tiniest pieces of thin aluminum. A heavy bag hung underneath at least stops a sneezing Japanese tourist knocking over the setup from 50ft but there is still a load of vibration. A heavy bean bag resting on top of the lens can only absorb so much vibration.
It really doesn't take long before such tripods are relegated to holding a flash or supporting your home grown garden tomatoes.
The more expensive 100-200 tripods are immensely better, but suffer most of the same problems to less extents. The difference is you paid 200 quid instead of 30. If you go for the very heavy steel tripods in the 200 range you can find some very stable setups that are not very practical outside a studio. Cheap Alu and carbon fiber tripods act as resonant frequency magnifiers for the inherent vibrations and are to be avoided like the plague.
You can choose 2 of cheap, lightweight, stable. Tripods that are not stable are useless so you really have a choice of cheaper (but not very cheap) and heavy, or expensive and lighter (but not too light as there is a minimum of strength and weight needed to be effective).