I did the fight twice (at level 4), both times without wiping.
The 1st time I went into it blind with PC lock, laezel, shadowheart and gale.
All party members were downstairs and I basically got jumped on. But I managed to win. Shadowheart being able to res with healing word as a bonus action was a major help and so was Laezel using menacing strike and a speed potion.
The 2nd time, I knew what was coming so I kept my party (PC dex Ranger, Astarion and Wyll) hiding, while I sent Laezel on her own to initiate dialogue and combat. It was an easier fight as I could a free shot in with all my other companions which basically removed one of the Gith out of combat. Moreover having the guys upstairs allowed me to shove on of the Gith of the construction for some extra damage. Once again menacing strike and speed potions are amazing in this combat. You can get up to 3 menacing strikes and thus chances to frighten some in the 1st round with action surge. Laezel is tanky enough to get them off.
The fight belongs to the more difficult fights of EA, but is far from impossible nor does it require cheese of meta knowledge. I assume the fight is intended to do at the end of 1st act so being level 4 (or even 5) is not unexpected.
And iirc, there is a thiefling who warns you of the Gith and recommends you of staying away from them. So there is some form of warning.