Helplessly dying during main story in Bravely Default

I've had trouble with all of the bosses in Bravely Default, especially with The Jackal and other side quests, with them taking over (And I'm not exaggerating) an hour as Jackal kept healing himself with the potions he stole from me, and me dealing absolute pitiful damage.

I was also stuck and had no way of passing Orthos, which I only won thanks to an Ablink with 9999 damage.

I was able to deal with the Turtle on the way to Sage Yulyana on foot by poisoning it and stalling out.

But now, my cheese strats are no longer working - which is quite a problem, as it was my only strat of beating bosses.

I'm in the middle of Chapter 2 where I have to get through Twilight Ruins to get to the Water Vestal, and I'm getting absolutely destroyed by the everyday common enemies there.

They're all weak to Earth so I made Agnes a Summoner, but that spell takes way too much Mana to use even once, and all enemies there take at least 2 hits of that to knock out properly.

On top of that, the Imps keep healing themselves while dealing nearly half of any team member's health as damage using Drain, and Silence turns my mages - the only real weapon I have against Imps - into sitting ducks.

This was how it was for me, on every step of the journey. I had to continuously run back and forth across the map to heal up at Inns, and that usually let me struggle through. But Twilight Ruins is my breaking point - I have to run back to an Inn every 2 battles, 3 if lucky. Items aren't a viable option either, as they're hella expensive and do next to nothing to keep my members alive as every enemy just cancels whatever potion I used anyways.

Am I doing something wrong, or do I just have to grind? Would very much enjoy a good answer, as I'm stuck on not even 1/4 of the game. My current team is Lv.24 Tiz as Monk(Lv8)-WhiteMage(Lv1), Lv.24 Ringabel as DarkMage(Lv7)-WhiteMage(Lv1), Lv.24 Edea as Freelancer(Lv8)-Monk(Lv1), and Lv.24 Agnes as Summoner(Lv4)-WhiteMage(Lv7).