It's not depend on device (at least it's true for the modern devices), Bandwidth is the main issue There is two scenario related to speed
1. if you live in area where you get full network but there is so many users around you then every user get very little bandwidth result in slow speed
2. If live somewhere there is few users but no network (Or Weak signals) then again slow speed
in conclusion a dedicated hotspot device not gone give you extra performance. But with hotspot device you can put them somewhere in good signal area(like balcony (I guess you can't stand there all day with your phone for just hotspot) ) and use Wi-Fi in your other device (this can improve speed if you are facing 2nd scenario)