Problem with 401K is that it's not inflation proof. Your Grandmother, presumably if she's old enough, likely remembers when she only paid $0.05 for a Coca Cola in a restaurant; whereas today, a Coca Cola costs up to $2 (if not $3 in a bar). Coca Cola increased 40 to 60 times within generational memory. The samething will happen to your 401K - it'll decrease in value by 20 to 60 times by the time you collect.
Holy Sh*t. Does that mean there are people who could have saved Coca Cola in bottles when they purchased them in the 50s and can now sell them for 4000% profit? Where are these early adopter soft drink mavens? They found the secret to beating inflation.
Inflation is certainly a problem, but comparing the last 50 years with the next is not meaningful economics.