比 is the positive comparison (A is more); 沒有 is its negative (A is not as X as B). Same pair, opposite direction.
弟弟比哥哥很高 → 弟弟比哥哥高 (no 很 inside a comparison)
弟弟比哥哥高很多 when you mean a small gap → 弟弟比哥哥高一點 (match the degree word to the size of the gap)
弟弟高比哥哥 → 弟弟比哥哥高 (quality comes last, after B)
English keeps the adjective up front ('taller than') and puts the standard last; Chinese sets the standard with 比 in the middle and lets the bare quality close the line.