Exactly, shatterpoint is way overrated, and really, I see no way of Mace winning this.
Kopekz thought he might be the sith'ari (the sith's chosen one) aka the ultimate sith and perfect/near immortal being after only just one conversation with Bane. Bane was untrained at this point, Kopekz hadn't seen any displays of the force from Bane, and he knew who powerful sith were (he knew of people such as Darth Revan, Exar Kun, Naga Sadow), yet he still believed that Darth Bane could possibly become the most powerful of all of them, so clearly he sense that the darkside within Bane was on the next level.
Githany believed his power was beyond the level of pretty much any jedi or sith master when he had only received a few months worth of training. The jedi and sith during those times were pretty uber (most martial order of sith, had been in constant war with the jedi for hundreds of years..), this speaks for quite a lot.
Kaan, the leader of the BoD was scared shitless of him before he had ever even met him; this was based purely on descriptions of his power, and Bane scared the crap out of him.
When he was 18, he was able to instinctively choke his father to death, which greatly speaks for how prodigious he was, and how strong in the force he was.
He once lost his temper, and was able to instinctively project his fury on an entire room full of people, and drive them all wild with fury; that speaks for truly how strong he was in the darkside.
He pretty much mastered force lightning after just 1 hour of having learnt the technique, and was even able to create a miniature storm. By BotS, after having grown much more powerful, he would likely be able to replicate this to much greater effect.
He was able to release a wave of energy that was able to collapse the entire 20 story Rakatan Temple, and the temple wasn't even hit by the entire attack (it wasn't hit by the portion that hit Kas'im).
He was able to effortlessly choke Quordis to death like he was a child in seconds, and Quordis was one of the top sith in the BoD, the head of the academy in fact.
He was able to control the power of over 20 sith lords combined with his own and direct it to destroy an entire world. This speaks quite a lot for his mastery and control by that point.
He was able to pull a moon out of orbit, and pretty casually too given he did it while riding on top of a flying beast.
He knew every move and sequence of the saber staff perfectly (and those are the moves and sequences for all 7 forms, and not just the regular forms, but Kas'im's perfected forms), and thus would be able to wield one to the same effect as Kas'im. He would be able to switch between these different forms, giving him a somewhat unique style.
Sirak, the top apprentice at the BoD Academy was incredibly powerful; he was able to move in blurs (those are Yoda speeds), had mastered multiple forms..and Bane was able to completely outclass him in saber combat; his shatterpoint ability was so great that he was able to sense weaknesses in Sirak's style seconds after the duel began, and constantly throughout the battle, but held back because he wanted to humiliate Sirak, and tire him down first, and towards the end, was able to tool him with one masterful manoeuvre; his movements were faster than the eyes of everyone present could see, so fast that it seemed like time had stopped for them. In other words, he was able to toy with and outclass someone as strong as Sirak, had the ability to end the fight in seconds, and constantly throughout the fight, and was able to move at speeds faster than the eyes of trained force user could see towards the end of a tiring duel. His speed here is incredible, and is much much greater by BotS.
He as good as defeated Kas'im in a duel; Kas'im was basically The master of the lightsaber; he mastered every from, every primary art of the saber, and then furthered and perfected each form and constantly refined his skills, and Kas'im was only able to defeat him when he used a style that was alien to Bane.
While he was choking Quordis to death, Quordis begged him to stop and let them fight with sabers so that he could die with honour, and Bane said that he would be able to just as easily defeat him with a saber, and Quordis seemed to know this. This implies that Bane would have been able to defeat him in seconds with a saber, and Quordis was one of the top sith of a pretty impressive order. It also shows that his saber skills were likely on par with his force abilities.
Bane possesses the orbalisk armour, which constantly pumps dark side energies and adrenaline into his body, and strengthens his muscles and keeps them constantly flexed. It's also completely immune to the cutting power of even a lightsaber, and covers his entire body, except for his head (the only area where he can be physically affected), and a few joints where the gaps are too small for a lightsaber to pass through anyway. It also heals non lethal wounds instantaneously.
His knowledge base was also pretty considerable too;
1. He pretty much knew the entire BoD archives inside out. The archives were huge, and contained much information regarding sith history and lore.
2. He had received most of the teachings that the then current Masters could offer via Githany. Nothing too great, but still something.
3. He had gained most of the knowledge (the most important knowledge at least) found inside Darth Revan's holocron. Darth Revan probably has the single greatest knowledge base with the exception of Darth Sidious, whatever he later found in Nadd's tomb, and the Ancients .
4. He was able to access a jedi holocron. This would give him a great understanding of lightside powers as well as darkside ones.
5. He was able to plunder the tomb of Nadd's holocron, and gain access to his holocron. This source of knowledge, by Bane's own admission, was even greater than Revan's, and gave him the power to 'play with gravity and orbits like a child might play with coloured balls'.
Until Mace can do that^, I see no reason as to why he would beat Bane.