It'll take the same time for that person who's stretched between many projects, since they need reports from the person they're managing anyway.
It will take more time for the two people since one more people will be included, but that's where opting-out is more comfortable than opting-in: you could have a discussion about the reporting part together and figure out what's most comfortable for everyone (whether it is only sending one person regularly or if both are there, etc). It can even be an opportunity for growth for the more junior person if they take on the reporting duty, since they'll have the help of someone more experienced and they'll hold more responsibilities than they otherwise would have. And all this can be decided by the people involved, who will know better than anyone else what they've actually done.
It's not about reporting, it's about decision making. Who is making the decisions? Who is deciding if a feature is worth postponing the deadline? Who is deciding when good is good enough? Who is deciding how to structure the teams? Should we write unit tests? How many? What should be unit tested? What's the software architecture? What DB to use? If you take any two devs there are a million things they'll disagree on. And someone just needs to make a choice.
For expediency, so you don't spend too much time bike shedding, and for consistency so you either deliver a polished and robust application late or a rough application on time instead of a half reliable, half polished application a little late.
Most of these decision should be made at the organization level or by a person full time on the team. And usually the person who makes these decisions(the product ones not necessarily the technical ones) also reports up the chain to make sure theses decisions are aligned with the organization.
Again, this is not an issue. You could make up a bunch of questions about pretty much anything, it's always going to be questions and answers in a management chain.
The point is that all this stuff can be answered by the two people as a team, and if they disagree they have to figure out a mature way to present their disagreement or manage to convince each other. If you're an experienced engineer and you think your solution is better than the junior's, then by all means just lay it out for your teammate to understand and accept it. If you can't even convince your teammate, I'd be worried about what you're going to do about your superiors all the way to the CTO.
Ultimately if there are a couple paths then you end up listing the trade-offs together as a team, genuinely, and you present THAT to your superior so that you can have a higher-level discussion about what they see and want from their perspective. You do the homework together, and you do it well enough so that your manager doesn't have to work for you.. Which you should be able to do anyway if you were about to be the manager, right?
It will take more time for the two people since one more people will be included, but that's where opting-out is more comfortable than opting-in: you could have a discussion about the reporting part together and figure out what's most comfortable for everyone (whether it is only sending one person regularly or if both are there, etc). It can even be an opportunity for growth for the more junior person if they take on the reporting duty, since they'll have the help of someone more experienced and they'll hold more responsibilities than they otherwise would have. And all this can be decided by the people involved, who will know better than anyone else what they've actually done.