rough, crude, coarse
麁 centers on a lack of refinement or precision: something rough, crude, or coarse in texture, quality, or manner.
麁 is an older variant form of 粗, combining 鹿 (deer) with a top element that may have originally represented something rough or coarse. The exact historical development is uncertain, but it likely relates to the idea of coarse deer hair or rough texture.
The top ⺈ looks like a rough, jagged edge, and the bottom 鹿 is a deer. Imagine a deer with a coarse, unkempt coat of fur that feels rough to the touch.
For ソ, picture a piece of coarse sandpaper that makes a rough 'so' sound when you rub it: so -> ソ, and the rough texture matches the kanji's meaning.