Lets Talk Cho'Gath
Let me start this thread by stating that I believe that patch 7.4 was a LARGE nerf to Cho'Gath, details to follow:
Relevant information: R - Cooldown 80 seconds (unchanged) R - Health per stack 180 -> 140 R - Health at 6 stacks 1080 -> 840
Math: To achieve 6 stacks before 7.4, it took 480 seconds and could be achieved by ulting any unit. To achieve the equivalent health that 6 stacks provided previously (1080), it takes ~7.7 stacks which I am going to round up to 8. 8 Stacks requires 640 seconds, assuming that you are able to feast conveniently placed champions or epic creatures on cooldown. So in the optimal scenario, it takes Cho'Gath 160 more seconds, and 3 champion kills to achieve the same level of effectiveness.
Gameplay: Before patch 7.4, half of the cooldown of Feast was restored when used on minions/non-epic monsters. This allowed Cho'Gath to ult around 40 second windows of inability which can be strategically planned (before recalling, after you kill your laner, ect). After patch 7.4 Cho'Gath is forced into large 80 second windows of inability that effectively reduce his map pressure by half (or more).
Why is this a problem: Cho'Gath used to enjoy a quick power spike in health that could be leveraged over opponents and made him an effective early game tank in addition to having only 40 seconds of downtime after ulting which leaves him with opportunities to kill his lane opponent.
Now Cho'Gath takes twice the time to scale, has more downtime, and can only accomplish the same amount of scaling if he kills multiple enemy champions.
What riot's stance seems to be: If you eat a champion every 80 seconds you can scale almost as well as meta picks.
What needs to change to revert this nerf: Health per stack needs to be increased to pre-patch levels. Minions need to reduce the cooldown by half again.