Then u saw the logs of some really shitty healers...
The proc for heroic is a max of about 25.8k hps. By comparison, a statstick is about a 4.7% increase in hps on the int alone for same ilevel. The math is comparable. If you're a shit healer, the cake is great as you can push a button and get on demand hps. If you're a great healer able to regularly do over ~550k hps, then the cake is an hps loss over a statstick. And on principle, I prefer raw stats over procs. So there would be very few fights where I would actually ever want a trinket like cake. if any.
Note: that's raid setting only. imo, for M+ the cake seems amazing.