I’m not really answering your question here, but the best PHP CMS IMHO is Processwire, bar none, and I’ve used pretty much everything under the sun over the last 10+ years. Nothing else gets out the way and let’s you get on with the job in such an elegant way. I like their model as well, they essentially support their development through useful and elegant commercial plugins for things like caching, form builder, pro drafts, etc. The caching module is really worth every penny and then some.
It’s got a beautifully simple API and templating system that really lets you tackle and manage projects how you want to tackle them.
We’ve had production sites with thousands and sometimes tens of thousands of daily hits running off it for nearly a decade and had pretty much zero problems with it that I can remember. I’m confused why more people don’t use it. Sometimes I wonder if people like to make their lives difficult and use the latest shiny new thing just so they can use the latest shiny new thing.
We’ve even utilised it in non traditional ways as well, due to its flexibility - for instance we developed a few games (UE4 and Unity) for clients where we set up and managed various game properties for objects, enemy behaviour, etc. that games could then easily pull in dynamically as JSON allowing a quick and easy way for non developers to play with underlying game variables while play testing with no real programming experience. The simple tree hierarchy system, supplemented with things like repeaters, standard fields and in built selector functionality really makes it easy for anybody to get a handle on it in under ten minutes and feel at ease.
We’ve integrated it with horrendously bad client SSO systems with minimal effort as well, to speak of it’s somewhat fringe abilities.
The community is great as well, no politics and very active.
Disclosure: I’ve got no commercial interests in it, other than it’s made day to day life much easier and I’ll sing it’s praises at any opportunity.