Lizard
Running gos without google play is an "involved" process that requires "regular" management of things. Its not set and forget. The initial learning curve with setup and finding the right apps and where to get them is also very steep and waaaay too much information to have to sift through. This step HAS TO BE done FOR them, and they can learn slowly over time afterwards.
"Normies" that are not tech savy and the "not willing" type (not willing to endure hardship of learning, no patience, etc) will not like gos without GPservices and will complain and revert back.
However if they are the type who are willing to "accept" at few nags and learn over time, if given a ready to go system, will learn the rest over time.
With playstore present things are much easier. However you should realize that YOU have to be available to them as tech support. It will invariably happen that something will come up, and you need to fix it FOR them and not expect them to do it for themselves.
The 75 year old grandma example, without question you MUST go with GPservices and also forget about profiles. This group even has a hard time with regular phones, let alone gos. In some way their lack of technical knowledge actually helps you hide many of the limitations of a privacy phone and often they are more easily satisfied with alternatives apps. They are less demanding about their app preferences, often cant tell the difference between app A and B, and only complain when something is not working.
Do understand that gos by default is lacking in some very important elements that the average person just doesn't know where to even begin with. ( store, calendar, audio/video player, keyboard, gallery, etc) also the black and white look WILL ABSOLUTELY put them off.
So the initial setup should be done for them, including possibly a replacement launcher if they have issue with the looks (though let them complain first).
So you personally need to have good command of gos and where to get apps, which apps to get, and how to setup. This way the extremely bumpy (cavernous) road can become a .... regular toyata corola ride.