𝗽𝗿𝗼𝗯𝗹𝗲𝗺+𝗶𝗰 → problem𝗔𝗧ic
𝗵𝗮𝗯𝗶𝘁+𝗮𝗹 → habit𝗨al
𝗵𝗼𝗿𝗶𝘇𝗼𝗻+𝗮𝗹 → horizon𝗧al
𝗽𝗲𝗿𝘀𝗼𝗻𝗶𝗳𝘆+𝗮𝘁𝗶𝗼𝗻 → personifi𝗖ation
𝗰𝗼𝗺𝗽𝗲𝗹+𝗶𝘃𝗲 → comp𝗨𝗟𝗦ive
(examples from Burzio, 2002)
Note that -𝗮𝗹 specifically does not combine with words that are already adjectives (sad→*sadal, strong→*strongal).
Historical shouldn't exist because Historic is already an adjective. Cyclical shouldn't exist because Cyclic is already an adjective. And so on: Classical, Comical, Symmetrical
We gain expressivity at the small cost of morphological irregularity
Unloosen - to loosen
Unthaw - to thaw
Unravel - to ravel
One day no one will notice Irregardless as unusual, either.