It simply means there will be stronger opponents than Kaido, well we are pretty much in endgame anyway, so BB, maybe Imu are well stronger than him or will be. Tho endgame doesn't mean the end is near, it could be an entire saga which contains years of content (5-8 years perhaps depending on arc length)
He gets captured. Him wanting to die is too fulfilling to him, he will have to suffer like the rest of the villains, witness their decades of hard work and dreams be crushed, death is an easy way out for Kaido not gonna happen, if it happens it happens much later.
His defeat will bring end to his dream and what he did in past 20 years
So, in a way his dreams will be crushed.
But oda made kaido WSC. He even went on to say "no one is alive to defeat him". Only exceptions I see to this are BB and Imu but even they will be under kaido shadows.
So him being alive overshadows many others characters who are waiting in line to for their time to come
Also, he is the only antagonist who has death flag.
Let me tell you why his death is significant.
Kaido was shown as someone who can't be killed. Someone who wished to die but this is because there is no one to challenge him. Thus, for him being at the top is boring because no one can beat him.
Once luffy defeats kaido and the latter gets the vibe that Luffy could be joyboy, he will not have any death wish. Infact, he will seek to live because he got someone who could defeat him and become Joyboy which he himself once wished to become.
So his death would actually not be fulfilling as you said. It will come at the most interesting time in his life. It will happen at a time when he will wish to live to see how things will unfold.
This will make kaido die unsatisfied and at the same time will create room for future opponents to get hyped