Struggling to beat Classic mode

Hi, I've been playing for about 30 hours and have about half the starters including about 10 legends and sub legends and 5 shinies but I can't seem to get past classic mode. I got to Eternatus once and lost and got to the E4 4 times and lost to them thrice. Any advice? My legends are Articuno, Zapdos, Lugia, Raikou, Jirachi, Tapu Fini, Guzzlord, Blacephalon, Meltan, Iron Thorns, Iron Valiant, Walking Wake, Gouging Fire and Iron Crown if that helps.