I recently took a full 6 from level 1 to 105 before I broke them off and swapped chars into my main group. Now, I did have plat to spend, plus a crap ton of TBM currency for upgrades. I made sure my toons were full defiant at every level opportunity I could equip.
WAR/SHM/BRD/BST/BER/BER. I didn't have any issues and was killing yellow to red mobs the whole time at the start of my camp areas, and would go until the first light blue came along, then switch camps. Shaman performed well enough, I didn't need the cleric. But...like I said, I geared all toons in full defiant so...YMMV.
My 1st group though was an additional Cleric. SHD/SHM/CLR/BRD/MAG/MNK. I rarely wiped, and I mean rarely. Only if I did something stupid. But I also lacked the DPS and kills were a lot slower. The Cleric definitely helped as I didn't have the gear.
I would switch the MAG out to another BER/BST/ROG and add a BST/BER/ROG. My personal favorite group atm is SHD/SHM/BRD (Holy Trinity), BER/BST/ROG. Very dominant in the current game.
In the end, play what you like and adapt to their strengths/weaknesses. The game is for your enjoyment. While we can offer opinions on our favorite, or universally accepted group makeups, choose what you like. Back in the day, I had a lot of Necro friends (I mained a Necro) and we would roll into Howling Stones and decimate the entire zone when it was still current content. Most fun I ever had in EQ. 6 Necros with Arch Lich and the level 59 spectre pets. Amazing!