The Deep Selector is excellent for quickly reaching an object inside a group without having to enter the group first. For quick edits, it is probably the fastest method.

The downside is that with complex artwork containing overlapping, nested, clipped, or stacked objects, deep selection can also make it easier to select something outside the area I actually want to work on.
Group isolation seems better suited to more involved editing because it establishes a specific editing context.
What I would like to see is Group Isolation developed into a more complete editing environment, where the isolated group temporarily becomes the active workspace.

Deep Selector
Advantages

• Quickly select objects inside groups.
• No need to enter and exit groups.
• Very efficient for simple edits.
• Useful when jumping between objects in different groups.

Disadvantages

• With complex overlapping artwork, it can be easier to select the wrong object.
• It does not create a protected editing context.
• You are still working within the larger document structure.

Group Isolation
For more involved work, I would like isolation mode to make the selected group the active editing context.
Objects outside the group could remain visible for reference but be temporarily non-selectable.
The Layers panel could also automatically focus on and expand the isolated group.
More importantly, I would like to be able to perform normal structural editing operations while remaining inside the isolated group, such as:

• Expand a warp or other live effect.
• Convert objects to curves.
• Add new objects directly into the group.
• Duplicate objects inside the group.
• Create new shapes, paths, text, or other objects.
• Perform Boolean operations.
• Change the internal stacking order.
• Create or modify nested groups.
• Add objects directly inside a clipping group.
• Edit clipping-group contents without leaving isolation.

Clipping groups
This could be especially useful with clipping groups.
If I isolate a clipping group, I would like that clipping group to become the active container.
If I draw, paste, duplicate, or create another object while isolated, it would be useful if that object could automatically be added inside the clipping group rather than being created elsewhere in the document hierarchy.
That would reduce the need to constantly move objects around manually in the Layers panel.

The distinction:
Deep Selector: quickly reach an object inside a group.
Group Isolation: temporarily make a group the active editing environment.
These would complement each other rather than replace each other.
Deep Selector would remain ideal for quick edits, while Isolation Mode would be better when working for a longer period inside a particular group or clipping group, especially when restructuring, expanding, converting, or adding objects.

When leaving isolation mode, everything outside the group should return to normal without changing visibility, locking, stacking order, or layer structure.

I think making isolation behave more like a temporary editing workspace would make complex grouped and clipped artwork much easier to manage.

This version keeps your full argument but makes the actual request more obvious. The strongest part is the idea that an isolated group becomes the active container, not merely something you can select inside.