Welcome to 5e.
5e was designed to be easily run & fairly light at the table for a Human DM.
This means, if you do the kite & kill that a Human DM would just have the opponents fall back & regroup for later instead of getting slaughtered piecemeal.
Hunam - 5 goblins (CR 1/4 or 50 XP - so 250 then x2 for numbers for 500) & 2 klaws (CR ~2 ish for the damage & HP, so, about 450 XP - so 900 for both x 1.5 for numbers and you get 1350) for a total of 1850. The threshold for 4 level 1 characters for a Deadly encounter is 400. Level 4 is 2,000. Level 5 jumps to 4,400 because of the second action gained.
Monsters w/reduced HP have negligible impacts on CR calculation, because it's all about expected damage output per round.
Per 5e rules, which this game uses, this fight should kill you 90% of the time, until you get to a party of 4 5th level characters. Then it is 'Hard' which is still "someone should die" territory.
Most encounters are pushing Hard to Deadly constantly.
