Ornn is still pretty good, and is actually at 51% winrate in diamond+, where you have teammates that will properly follow through on initiation and will take proper advantage of Brittle reducing tenacity.
The challenge, though, is getting the hang of how to ult and aim properly (long range is the best), as well as the timings of his skills, like when trying to cast his E, or finding the proper use of W in a fight, whether damage, debuff, shield, or ignoring CC...or all 4 at once.
For example, W can negate Yasuo’s tornado and Riven’s knockup, but you have to balance that with how those champs will try to fight and land so you can at least hit them with the last prt of W.
But with Yasuo, and even Braum to a degree, you have the challenge of ult vs windwall...unless you can bait out the Windwall, he’ll always screw you over.
But personal opinion, he’s very worth it to learn, and I’m both excited and nervous to see how preseason and meta shifts affect him, especially after the buffs he was given.
Just a recommendation..be wary of Courage of the Colossus/Aftershock for keystones in old mastery and new runes sustems, respectively. If you happen to hit a target at a distance with your ult, it’ll proc the keystone, which then falls off before the battle really starts.