He was REEAAALLLY vulnerable in physical point especially being unmoved after giant sword impaled him to the ground and he pulled it out like nothing. Don't mix in real difficulty of the game and actual lore.
And even more in mental. So vulnerable that he went all "You ****ed me and for that, Mundus I kick your ass one on one into another dimension" which he proceeds to do.
People should replay game and actually check that Dante was over the top character since his first introduction surviving being stabbed and managing overcome even worst kind of situations. For all I know DMC3 Dante got his ass handled much more often and in worst manner than anything DMC1 Dante made in DMC1.
In the actual lore, though, the only reason Dante survived the impalement at all was because he was wearing his amulet, and the amulet had his mother's soul haunting it. He died as a child, Eva revived him. He (possibly) died right there during the Alastor acquisition scene, Eva revived him. He was going to die by laser beam, Trish channeled her inner Eva and saved him. Trish died, Eva revived her just as soon as Dante got the amulet on her corpse (so basically Eva saved Dante yet again). And right at the end, he was very aware that he could die in Mallet's explosion without Sparda's awesome power to bail him out and decided to go out fighting.
"The gate has been opened. Dante, you're not getting away. This is where you will die."
"I'm not going anywhere. Besides, there's no place
to go, look around! This'll be your burial ground as well!"
DMC3 or 4 Dante wouldn't have had that moment, and Capcom completely removed Eva's involvement in later mortal situations by having Dante survive impalement normally and turned it into a running gag of the series.
So yeah, that's "actual lore" for you.
Anyway, yes, about DMC5. it's best that Capcom admits DMC2 happened and that Dante's trapped in Hell. That's the perfect set-up for Dante traversing all the circles like his namesake, and introducing a new non-Mundus overarching enemy. If they
have to, they can probably milk some plot out of it by saying it's the devil that
really killed Sparda, and Mundus was just the fall guy.