Long post incoming...
The new features look like they solve enough. It seems like it is basically the missing piece of the puzzle. You have authentication, authorization, throttling and parametric middleware coming from the framework. Packages are very nice and sometimes they solve cumbersome problems. However, I think that sometimes people are too quick to jump and search for a package these days even for things they could easily achieve on their own and with better flexibility.
Sentinel is nice and so are the other packages. My advice is to take some time and explore the framework. Give yourself time to know what you have at hand. Yes that includes spending some time on it, but don't think of it as lost time. It is time gained from avoiding future frustrations. If you want to use Sentinel or any other thing, go through the code. Make sure you are comfortable with how it is doing what it is doing and that it sits well on your project. Never let a tool define your project.
Laravel code is so well documented that you can read through it easily. Tons of small things that can make your life easier that maybe are not even in the general docs. Read through the docs, but do go through the API Docs every now and then when time allows.
I might have spent countless of hours trying to debug packages that do not play nice together, that do not play nice with Laravel, that do not do what they are supposed to do for reasons that are a total mystery even to their creators.
Use packages that do not try to do too much, that you understand the code and that the code is well documented. Packages should save you the typing, not the thinking. Furthermore, creating crucial dependencies on third party packages might provide challenges when you try to upgrade Laravel to the next version. I see many users going through packages and spending days to find a fix even to simple CORS packages are not doing what they want, when writing a CORS middleware yourself does not take more than 15 minutes. Yet they bang their heads against the wall trying to make the something they did not do make work for them at all costs.
There is nothing Sentry/Sentinel has that you cannot make it and twist it to your liking with the current tool set offered by Laravel. Before even thinking of any package, do yourself a favor and think whether you actually need one.