After reading Renza, I'll admit I'm a little curious what hard mode is like. Poor Renza managed to get utterly screwed over on easy mode.
Honestly the Witches are actually easier to fight than the Daemons. There's only one, you have to actively track it down and breach your entry and for the most part they'll ignore or avoid you unless you kick down the door ribbons blazing. A large part of a Witch's psyche and hostility is that they used to be Magical Girls, remember; they'd naturally avoid Puella normally if they could get away with it (which they can't); they naturally tend towards isolated places of suicide and despair, where no-one will look for them. Witches you can play divide-and-conquer, the danger in letting them build up is that that's how things like Walpurgisnacht happen (and also, y'know, social instability due to suicide cults and disappearances and such). They're maddened by despair, in their own private, 'safe' little worlds. Putting down a Witch is an act of
mercy.
Daemons, by contrast? They're spawned from the grief and despair of Humanity as whole. They posses a malevolently animistic sentience in the same way Witches do, but without the 'fallen Magical Girl' part that gave them human weaknesses. They might be weaker individually but their spawn rate is a lot higher (as in 'by total human population', not 'dependent on Puella Contract rate + Familiars'). This means they have numbers on their side, fight sensibly, recognise the Magi as their natural enemy and will totally gank the shit out of you given half the chance. Daemons fight smart, set ambushes and traps, abuse their ability to phase through walls to cheat and reposition like bastards, and there are
always more of them than you. It is perfectly possible to wind up in a situation where they're spawning faster than you can kill them and one day, suddenly there's a horde on your hands. One on one, a Puella will kill a Daemon every time (which is ironically why they don't hide in Labyrinths/Barriers; they're too weak to put one up individually), but it's the one you miss, the one you lose track of whilst being hounded by the others that gets you.
Daemons hunt the Puella as much as the Puella hunt the Daemons; they're a very different foe to face compared to Witches, which are more like one-on-one duels you can approach carefully. Really what makes Witch-mode harder is 99%
'fucking Incubators' more than anything else.
Doesn't do Renza much good because she is/was stuck in the unfortunate situation of being the sole Puella Magi in a big, angry city, but the the answer to 'Daemons' is generally 'teamwork' and 'have someone watching your back', which is a concept Witch-verse leaves crippled with an arrow to the knee.