“. . . man-portable antitank missiles can penetrate 800mm of armor steel?” That is 31.496063 Inches! Hellofamissle!
BBs may have been vulnerable to missiles, but smart bombs took over the role of the BB for land bombardment.
Before smart bombs, BBs put the fear of God into the bad guys back in the day! 2700 lbs of high explosive will ruin your day!
And, by the end of their life cycle, the 16” naval guns were very accurate!
IIRC the BBs were mothballed (1992) before the bad guys had missiles that were effective against them.
Negative - Exocet came out in 1967 and can penetrate somewhere between 54-72 inches of armor, depending on a number of factors. Exocet is considered a smallish antishipping missile. A heavy capital ship antishipping missile (like the Russian Granit - SS-N-19 Shipwreck) can penetrate over 140-150 inches of armor. The Granit came out in 83, and its predecessors weren’t a lot less capable. Shaped charges are amazingly penetrative. So, no, the bad guys had missiles that were very effective against them well before retirement.
Exocet and all the other missiles in the world arms market are why surface combatants are only armored against small arms from the 60s on - there’s no point to WW2 style armoring when no practical amount of armor will stop an antiship missile.