Rikuto
P-P-P-P-P-P-POWER!
Leon is not ALL slow hard hitting strikes he also has one of best pressure strings of all the grapplers with his p6p/p,k,or 2k and 6pp/p,k, or 2k and from what i remember all mixup options from those strings are safe. not to mention 2kk is great at opening an opponent up and breaking their defense. He also retained 33p and its properties in 5U giving him a good ranged sitdown stun that high crushes.
Lets not also forget like the rest of the grapplers getting hi-counter thrown by Leon means you'll be eating a shitload of damage accept unlike the other grapplers Leons damaging throws hurl them a good distance for potential wall/dangerzone damage on top of the already high damage like dervish throw and desert falcon
He was mediocre in 4 simply because ALL the grapplers got fucked in that game so if they use his DOA3 iteration as a template along with taking advantage of 5's mechanics with some good guaranteed set ups then i can easily see him being mid tier at worst.
Leon's frame advantage super pressure is unlikely to ever return to the levels of 3.1.
I would expect him to play similar to 4, but with a lot more environmental control and guaranteed damage setups.