Get DMC3SE, don't bother with vanilla DMC3. Agni and Rudra + Cerberus were tough battles, mostly because you don't have some of the better moves in the game yet. There are some tough boss battles after that but it doesn't really get super hard until the last boss fight Vergil which remains as one of the best boss fights in action game history.
And yes Dante has quite some moves in DMC3 that aren't in MVC3 plus one weapon (Spiral) that wasn't even used.
Like for example, he basically has a style that allows him to summon a clone like Zero. And he has another style that allows him to slow down time like Amaterasu.
If they also incorporated Royal Guard with Dante in MVC3, then he would automatically be God tier. Imagine having a character who builds up damage for every Advancing Guard and then releases that damage in a really fast, invulnerable dash (a hyper let's say) that takes at least half life on your character.
With all the tools that Dante has in DMC3SE, he still gets blown up by Vergil.