I think there is a few things we are not taking into account:
1) Bunta's past
2) Bunta's eyes (here me out)
1) Bunta used to go racing with his bodies back in the day (he wasn't limited to just Mount Akina). Bunta never lost a race as he was considered the "undisbuted, couldn't be beat" racer (Cf. Stage 1 Act 1 - he ultimate tofu store drift) only one person really giving him a run for his money (See Stage 3). I remember reading somewhere that in the manga Takumi's mother died while delivering Tofu, and the reason I bring that up is because in stage 1 act 24 when Keiichi Tsuchiya calls Bunta about the race between Takumi and Ryoske, Keiichi makes the comment about Bunta scarring him for life with his "monstrous drift" to which Bunta replies "that was a long time ago". Whether retired or perhaps with a vow never to race again, atleast not in a more active sense, this is why we do not see Bunta race.
2) There is a reason that Bunta is the only one in the series that has his eyes closed. Its more of a symbollism, a sort of literary device if you will. In essence, Bunta is the perfect driver. This does not mean he is the perfect human being, but rather that he is the "undisputed, couldn't be beat". For example, whenever anyone asks Bunta about the outcome of the race, he never says anything except "we'll see after the race", representing his calm, collectedness. During the battle between Takumi and Godhand Bunta never makes any calls on the race, but he remarks on how Takumi still has a lot to learn. In Stage 3 when Bunta is driving the 86 for the deliveries and passes by Takumi's challenger, Bunta remarks "there was some skill behind that wheel" demonstrating his sort of 6th sense in racing. Overall, Bunta's eyes, as a literary device are to show him as the only driver who hasn't been beat. Although there have been some who gave him a run for his money, i.e. that have come close to beating bunta - Bunta still comes out on top.
Also, just going to throw this in here since I mentioned it - but yes, Bunta would beat Godhand. Godhand admits that an 86 has the ability to beat his time on the mountain, and we even see Takumi getting close to defeating Godhand, Bunta also remarking that Takumi has a long way to go. the point here being that comparing the skill level of Godhand and Takumi and the result of the race, it is likely that Bunta would win, most-likely by not letting God hand over take him the same way he overtook Takumi.