my take from a while back:
TL;DR: maximum for pure Open Era (i.e. no crossovers from amateur era like Laver or Ashe) is #12, personally would put him around #15
the Open Era career win % list is a good start (for reference: Medvedev is at 75%, but goes up to around 79-80% if you filter starting somewhere in '19)
Medvedev is never passing Djokovic, Federer, Connors, Lendl, Laver, McEnroe, Sampras, or Agassi
assuming you look at level and not just major tallies, he's certainly not passing Edberg, Nadal, Becker, or Murray
you then get to the Ashe, Roddick, and Mecir trio. i don't really rate Roddick outside of '03-04 and '09-10, but he was doing the same "get to The Guy" bit, so i'd say Medvedev is in the same general elite to ATG range but a bit higher
idk if Ashe ever really tempered his game to the necessary degree for sustained hard court success - his best wins were a decider against his pigeonizer Laver in Tucson '74 (before losing to Newcombe), a decider against Nastase in Paris '75 (before losing to Okker), and a straight setter against Borg in the WCT Challenge Cup (before losing to Nastase). feels like he just couldn't keep it clean or consistent against top competition
Mecir was an overrated fraud. Medvedev would be justified in calling him a small cat who doesn't know how to serve fight
moving down the list for some argument material:
i would argue that Rosewall was clearly better. just looking at the Open Era, his win % goes from 73.8 to 76.9% if you stop at the end of '74, when he was 40 (!!!), rather than including the ~70 official matches he played up to '80. on the pro tour in knock-out tournaments with more than one set, he won hard court titles beating Trabert and Gonzalez once each, Hoad twice, and Laver thrice (two of those wins in Laver's peak year of '67). and obviously if you have a GOAT-tier backhand you're going to be an ATG hard courter
Courier and Wilander have more majors if you care about that. i would say that Medvedev is a clearly better server and returner than Courier and across their careers is a comparable baseliner (but '91-93 Courier clearly above). i'd say Wilander is a clearly better baseliner and net player and comparable or slightly better returner, but much weaker server. would tend towards Wilander >> Medvedev > Courier
if we want to talk about bad luck/flopping in hard court slams (depending on who you ask), there's Borg. injured in '78 and had to go against Connors, upset by a servebot in '79, lost a decider to McEnroe in '80, and lost a messy match to McEnroe again in '81. i'd lean towards flopping, and i think he wasn't always consistent on backhand depth and return potency, but i could see an argument based on his competition and his dominance against the field
for big serve & forehand guys, there's del Potro and Newcombe. playstyle wise, Newcombe certainly had the skills to drive Medvedev insane with his net play, but overall, i don't think he was all that great against top competition. meanwhile del Potro's slam was clearly much more impressive (demolishing Nadal before pulling it out against Federer), along with other '09, '13, Olympics, and Davis Cup results, so i'd say del Potro >> Medvedev > Newcombe
then for surprisingly aggressive retriever types, you have Hewitt and Chang. Hewitt has the slam while Chang doesn't, and after a certain point both of them were pretty impotent against top competition. i rate peak Hewitt and how he dealt with Sampras pretty highly, but he just fell off so fast with his injuries and not handling Federer... ehh would still say Hewitt > Medvedev > Chang
finally you have Alcaraz and Sinner threatening to overtake Medvedev by the end of all of their careers. not guaranteed, but certainly looking quite likely
rest of the hard court slam winners: Thiem, Cilic, Johansson, Kafelnikov, Korda, Wawrinka, Safin, and Rafter. briefly: peak-wise i only rate Safin and Rafter, and none of these have enough consistency for me to care about them as ATG hard-courters compared to Medvedev
bonus round, let's also add on some pre-Open Era players: Gonzalez, Kramer, Budge, Vines, and Tilden were all clearly ahead
all in all, Open Era hard courters based off their careers to date:
higher tier than Medvedev: Djokovic, Nadal, Federer, Murray, Agassi, Sampras, Becker, Edberg, Lendl, McEnroe, Connors
comparable tier to Medvedev: del Potro, Roddick, Hewitt, Courier, Wilander, Borg