Yes but one of the key things about subagents is they keep all of their tool calls and exploration out of the parent context.
If you plan on continuing on in the parent, and aren't going to necessarily be touching the systems the other agents are exploring, it can be worth it.
It's useful in certain situations where the parent context may need the "10,000 foot" view of something without going back in there. But subsystem-specific AGENTS.md/CLAUDE.md files are still superior and accomplish the same thing. The problem with those is they can become stale.
They are just making the point that it makes sense that subagents would use more tokens because they have none of the parent's context.
It seems like there could be a useful strategy of writing a plan with a main agent, and then instead of spawning subagents to implement, fork the main context to write each part. Then use one last fork to verify the work. That way you keep reusing the same context without polluting your main context for when you are ready to continue.