The idea is not to give a small bonus, which change nothing. +20 % is not a game changer.
+100 % is a game changer, it means few Jotnar units, with first attack promotion, can achieve a high strengh, and defend really well.
I proposed this to try proposing something which boost their defense, and feat with their nature. Having stone wall it's extensive, it need the fortification tech. And destroying the fortification will be possible with siege machines.
It's just a free idea, no necessity, it depends of your feelings of what you want to do with this race.