Many development project don't need a 'rock star'. They can be done with "typical" architectures, existing frameworks, and just need "assembly-line-type" workers for all of the steps. I'd even say "most" projects are like this and any project can survive without a rock star.
There are also different types of 'rock stars' and they can help on even the most basic project. In general, the 'rock star' can do any/all of these things, but what do they do on a day to day basis varies based on their individual "specialty"
* some can architect the "difficulty 10" projects so it can be implemented in assembly-line fashion by "typical" developers
* some can implement the "difficulty 10" projects that wasn't architected well (when a team of N "normal" developers would end up with a late and buggy implementation)
* some can debug like nothing most people have ever seen (they don't usually create difficult-to-find bugs but are a huge asset to the team when the bugs come up which can happen on even the most trivial project)
* some just implement so well (speed of development + lack of bugs) that they literally will be cheaper than a team of N people (so, to the manager they aren't necessary but would be preferred)
* some can mentor, and find other people's strengths, and reorganize efforts on the fly. they can help everyone else be more productive, and can adapt the process/team as requirements change and can be critical to delivering on time and above requirements especially when things go wrong.
* some can help where ever needed (front-end, db, back-end, sysadmin, security, build, etc) and can step in without losing a beat when another member of the team is out (sick, vacation, left for another job).
* some can find bugs in 3rd party libraries or system components (without the source code). find workarounds and/or patch those libraries to continue development quickly while sending the bug fix and appropriate level of explanation to the library developer to get a permanent fix. If you've ever been on a "difficulty 5" project which found a show-stopper bug in a critical 3rd party library during QA, you'll really appreciate this skill. I have seen one case on a "trivial" project where this skill was necessary and a few other cases where it really helped.
I've worked with a very small number of "rock stars" over 30 years. They all had multiple of the above skills. I've worked with 3x as many people who were considered "rock stars" (by themselves and sometimes others) but weren't. In almost all cases, the "fake rock stars" slowed the project down more than they helped and the team would have been better off with one less member.