It never occurred to me to do hanging things separately.
Underwear gets perfectly clean using warm water as long as you are using soap/detergent. Don’t forget that it goes through the hot dryer too.
I used to do it tog but it got so annoying as my family grew to pull out the hanging stuff when everything was wet from the washer. Now I have enough for a full load of hanging stuff so it makes no sense to not do it separately