Methadone withdrawal isn't fatal. No opioid has fatal withdrawal symptoms. Anyone that tells you that doesn't know what they're talking about or is actively lying to you. And frankly, it's a lot better that people use pharmaceuticals recreationally. They're of known purity and strength, which makes overdoses less likely, and for opioids, protects the user from long term effects. Most opioids are safe to use basically indefinitely and have few, if any, long term detrimental effects for your average person.

You can't make the claim that drug A is more or less addictive that drug B. Addiction has little to do with the substance used as far as is known and there is no way to measure addictiveness objectively.

Also, methadone is used because it's legal, politically safe, and has a long half-life. The long half-life is useful because the person using it doesn't need to dose as frequently and it lets politicians and addiction treatment professionals pat themselves on the back because they got the patient off of heroin.