He definitely wouldn’t have let them do that shitty plan in s4. 

i'll say it again but you could literally just copy paste this into s4 and pretend he's reacting to their next plan

because even if they actually managed to burn him to death against all odds then like, what? there's small gates cracked open all over town now, and there's still a giant cosmic shadow monster living over there that's not averse to possessing people. just burning him isn't really a solution to their constant UD problem at this point

their big plan in s4 was just doing what they did in s1, and s2, and then wanted to do in s3 again but Mike told them not to, AGAIN. and shockingly it still didn't work

to be fair s4 had an additional final step to it with Nancy actually considering that the fire might not kill him so she'll... shoot him to death. with the guns that famously don't kill anything above small demodog size at best...

which is actually just her plan from s1 with the Demogorgon again i'm just realizing??

no one has original plans. the sauna test was the last shred of plan creativity that also actually did what is was supposed to and that was a whole season ago (and that might just be because it wasn't a "let's literally just kill it with fire immediately" plan which is what 95% of the other plans people are coming up with are, when it turns out that the UD is still causing them problems after... they tried to burn it to death the last time)

they really don't need Will or El to figure the UD out right now, they need to start small and primarily need someone to look them deep into the eyes and tell them that they're being fucking stupid again

if someone says, let's just burn the entire Upside Down this time in s5 i will lose my fucking mind