Hard to say, but I think Mosconi would be a top player today.
I have seen the debates about that and really don't want to get into it.
I also think he would be using modern equipment.
I am not a serious player and have not been for a long time. I just enjoy casual play. So, although I consider trying a CF shaft, I have no great compulsion to get into the modern gear. I am a cue afficionado and collector.
It looks like the mass producers and custom makers are addrressing the market demand for butts that take extensions.
If a player wants one and has an older cue, they can have it adapted or buy a newer cue.
More or less I am just amazed at how much has changed. Even more, some of the things that were criticized in yesteryear, ar now becoming accepted and even standard.
In my EDC case I have play, break, jump, and masse cues, and I carry my own bridge head that I have has since the 1980's. I have more than enough gear for enjoyable casual play. At home I have carom and snooker cues as well. But I have over 200 cues, so sometimes I just experiment and compare cues.