Rock and Austin went mainly off scripts, in terms of improvising Rock was the stronger one but never just a completely improv guy. This is the reason Cena is probably the best actual unscripted talker, because he spent over 10 years just going out and doing promos, using bullet points for most of them and doing the 10-15 minute segments that Rock and Austin and Hogan never had to do. Even CM Punk was better at this which is why he actually tore up Rock for a moment when he just spoke to him, and Rock couldn't answer back with anything as good so he had to stick to his prepared promo, which made no sense to go back to after Punk just called it out, but luckily for Rock the fans won't choose Punk over him so Rock still won with the live crowd without anything to really offer in terms of the verbal exchange.
Hogan was an amazing promo, but you just can't see him winning a real promo battle.
It's from the Hogan era to the end of the Attitude Era where they kind of killed the need to talk on your own, but if you go back, Roddy Piper, Lawler, Cornette, etc... would absolutely tear anybody up without needing a second to think.
Strange how that came full circle with Cena and because he could be so trusted with the PG thing they just let him do what he wanted and he developed the skills that some of the biggest names ever didn't completely have.
Roman was total shit at first with the Vince shit, but he got more freedom and got way better, but even during Cena's last return, Cena had to set things up so Roman could 'own' him, like the missionary line which Cena explicitly set up for by spamming catch phrases which he never goes that hard on.