Just wanted to point out a couple things about hashirama's level of regeneration.
Of course he has shonw he can be KILLED by JUST a KUNAI despite having AUTOMATIC REGENERATION here:
Despite having AUTOMATIC REGENERATION, Hashirama still with enough chakra to control his buddha summon and suppress the kyuubi as well as bring it back to Konoha to be sealed within a JINK.
Hashirama was just bleeding, bruised and battered very badly showing the limits of his regeneration Here:
Obito right side of his Body is senju hashirama's and also has Automatic regeneration without using hand seals as shown here where the rasengan that hit his arm and scuffed it up was able to regenerate.
However, when kakashi stabbed Obito in his body with a chidori kunai, the automatic regeneration was not able to do squat against such a level of damage which was shown by Obito being forced to absorb the Juubi just to heal his wound to survive as well as become the next sage of six paths Juubi JINK.
Hashirama's automatic regeneration is LIMITED to cuts (slight or deep), bruises, low level burns and that is about it. He and his regeneration abilities has not shown the ability to regenerate organ tissue, organs, ect.
Meanwhile tsunade's automatic regeneration can easilt regenrate organ tissue and complete organs if need be PROVING her regeneration is far greater then hashirama's as proven by hashirama's low level regeneration feats.
So as I have been claiming and the Manga PROVES. Hashirama's automatic regeneration is not near as effective as tsunades's. ANd hashirama ONLY being bale to heal cuts, scraps, bruises and burns explains why hashirama CAN be KILLED BY A KUNAI, which is why he was going to commit suicide with one.
And so, if an enemy can stab him with a Kunai deeply, hashirama will in all likelihood die without assistance from another medial ninja.
SO QUIT ACTING LIKE HASHIRAMA HAS THIS AMAZING INSTANT REGENERATION BEYOND TSUNADE'S WHEN THE MANGA PROVEN HASHIRAMA'S PALES IN COMPARISON TO TSUNADE'S ONLY ABLE TO HEAL CUTS, BRUISES AND BURNS AT BEST, NOT ORGANS, NERVES ECT, THUS WHY A KUNAI IS MORE THEN ENOUGH TO KILL HIM!!!!!!!!!!
Minato vs hashirama CONCLUSION:
Since Minato WILL be able to at least TOUCH hashirama (especially using kage bushin which makes it FOR SURE hashi is getting touched at the least), and since after that minato can directly instantly blitz hashirama with a KUNAI before he can possibly react (not even V2 supermode raikage could), which is canon enough to kill him.
Then minato can actually win without having to resort to a draw using the shiki fuujin Add in fukasaku+shima summon for powerful sage technique and FROG SONG for insta-win Genjutsu against an army of Mokuton clones coupled with the use of 10 kage bushin's, each able to do exactly what the original can meaning hashirama cannot possibly compete.
And since MInato has seals/Tag all over the fire country as well as other countries to use for teleporting to in order to avoid huge scale attacks. Hashirama CANNOT Possibly HIT Minato or his clones while minato and his clones can hit hashirama pretty much at will using hiraishin level 2 and 3. Then once tagged, can all hit hashirama at will instantly without a doubt which measn hashirama cannot possibly win against such overwhelming attacks.