Is the UN Security Council losing its credibility due to the monopoly of big five?

since its inception in 1945 there has been no global, or even regional war nearly on the scale of WW2.....and that was pretty much the purpose of the Security Council...

...the vast number of regional conflicts and proxy wars that have ravaged various parts of the world are considered "acceptable" by the UN as a whole because their role is to preserve an overall "status quo"....

something to think about the next time you want the government, government agencies, politicians and bureaucrats to "save" us from anything...

When did the Useless Nations Security Council ever have any credibility?

No,
It was lost years ago.
Requires unanimous decision.
Not even the US vote to enter WW2 was unanimous.
Requiring unanimous is a great way to ensure nothing gets done.