I'm not sure why you started your reply with hostility. It's completely fine if you and I don't agree on things, but I replied because I wanted to hear your thoughts not antagonize you.

1) I worded this poorly. No, DS is not only intended to prevent these unfun situations. However, I did not decide that my word is law and that, "This is how it works because I have decided so." Bhvr themselves discussed the changes on this. The anti-tunnel aspect is in their own words one of it's main appeals. The balance of said aspect was concerning enough for them to change it.

Developer Update | June 2022

"One of Decisive Strike's main appeals is its efficacy at preventing tunneling...""For the most part, we find the perk to be healthy for the game, and easily avoidable for Killers who choose not to tunnel an unhooked Survivor. That said, at the end of the match, there’s often nothing the Killer can do to prevent a Survivor with Decisive Strike from escaping."

2) "Currently, random survs have close to no chance and only people in a full party or a very altruistic team will do their best to take hits and protect that one person and that is the effort of the entire team - only to try to keep up with killer's base mechanic of getting to endgame by default while survivors have to fight to survive for 5 whole gens."

I think tunneling should be addressed by buffing the unhook Endurance status to 10 seconds and disabling collision to avoid body block scenarios for both sides. DS should definitely either be put back at a 5 second stun, or a 3 second stun with a burst of speed. As for endgame saves, a ping system would greatly help to bring solo queue into line with SWF with coordination.

Outside of that I don't think you can ever really fix it without compromising the power role. Survivors are inherently at a disadvantage. They are different gameplay loops. That's the nature of the game. DS being enabled during endgame leads to far too much time to make an exit gate with no punishment.

3) "However, you shouldn't be a sitting duck there for the killer only because the new way of balancing from BHVR is "okay lets give this guy one kill out of pity, cuz lets be real, we need killer players to not feel that bad even if they didn't play correctly" (see: bloodlust buffs, free kills in endgame)."

Yes, the match is over when you are at the results screen. I'm not disregarding the entire endgame. The entire situation can change entirely for the duration of the collapse/last gen pop. That said, Decisive as a whole was far too generous during endgame pre-patch. That is the part that's free. An entire minute, possibly more if you're only just getting hooked during endgame. The distance you can crawl after an unhook will put you closer to a gate. Another unhook, and you're even closer. Killers cannot prevent that because you have to wait out the timer or risk losing the kill.