Well it did took me a pretty long time clearing World 4 having stuck at 4-4 for months until yesterday when I finally decided to watch some guides online. I'm still really surprised and now a little stupid with how people beat that stage with only 3-4 operators. I guess this is the difference between knowing what terrain the stage is and just going with the flow. XD
Not gonna lie though from 4-4 to 4-10 (the last stage of World 4), my 2 6-star operators really did their wonders (as well as my 2 6-star healers). If I didn't get those 4 6-stars last month I probably would be stuck at 4-5 anyway. XD
Now I'm trying to beat World 5 and having a hard time with it. I think it's pretty doable though once I level up my 6-star operators to max level and promote them to ELITE 2. At the moment, I'm short on LMD and materials so probably would be grinding this month again. XD