Opening up a sensitive sequence without using PRECOMPOSE

Agree with Rick - if you "Never had good luck with Pre-Comps", you're probably using AE wrongly. That aside, why should just pre-composing stuff foul up anything? The rest only makes my head spin. A screenshot of the whole thing could probably have told us everything in under three seconds. That and of course for just sliding layers around precisely there's already scripts on AEScripts.com like this one: https://aescripts.com/rift/ . There's a whole lot more as well.

Mylenium

70 layers, each 5-seconds long. Sounds like you are trying to use After Effects as a video editing app. AE is not, never was, and is not intended to be an NLE. The average comp in a professional environment is one shot. Most shots in most movies are less than 7 seconds. If the only way to do a transition between two shots is in After Effects, I will put the two shots in a single comp. If there are 3 shots, I create two comps that will overlap shot 2. I almost never have a comp that is longer than a sentence or phrase, 4 bars of music, or a single dramatic event. The final editing is always done in an NLE. 

 I work on a lot of comps that have hundreds of layers in dozens of pre-comps because I need to manage rendering order, use procedural mattes, isolate 3D elements, and do a bunch of other stuff that is impossible in a single comp because AE starts calculating pixel values at the top of a layer, moves down through masks, then effects, and finally transformations. When that layer is calculated, the calculations start on the next layer. Pre-composing is like using Nodes in a node-based compositing and animation system like Nuke or Davinci Resolve. It is a necessary and useful tool that simplifies the creation of complex composites and animations.

If you have the Labels column open and you Ctrl/Cmnd + select multiple layers, you can assign them all to the same label group. You can select the entire label group by selecting one layer and choosing Select Lable Group. You can then grab any one of the selected layers with the Selection tool and drag them to the left or right in the timeline. I use label groups all the time, and I've never had a problem repositioning a bunch of layers. 

If you move the CTI (current time indicator) down the timeline to a new starting point for the selected layer in the Label Group and you hold down the shift key, the in or out point will snap to the current time of the CTI. The layer you are dragging will also snap to the in or out point of any other layer or any marker on any layer or in the comp panel. I use Label Groups and markers all the time to move 10 or 20 layers and nested comps (pre-comps) to a new time. Lable groups make it easy to select layers 1, 3, 9, 14, 27, and 30 move them all up or down the timeline, precisely snaping the layer you are dragging to the in, out, marker, or keyframe of any other layer or the CTI.