Basically yeah. +5 cold is like +5 strength (so 19 +5 cold is like a strength 24 unit) - except it's not quite as good, because there are certain units naturally immune/resistant to certain elements, and there are also promotions you can take to add resistance. Vulnerability also exists, but it's much much rarer. Just think of it as +5 strength that will occasionally be reduced/ignored when fighting certain units.