It's not people being ungrateful, it's a completely natural and expected reaction to being let down.
Imo just make the roadmap private and completely eliminate everyones expectations. I must admit, from a business perspective it's a bit shit to let paying customers see the roadmap with these features on, keep them interested, get them excited enough to keep them paying their subs, just to pull features at the last minute. You set yourselves up for a case of over promising and under delivering. Which is never good. If I did that, i'd fully expect my clients to be disappointed and at worst, not bother coming back.
Tone Mapping was the one feature I was waiting for, that and fixing displacement. The only reasons I've kept my subscription alive and not switched yet.
Like people have already pointed out, it's mostly disappointing because these things already exist in other available engines and have done for some time. We're not expecting something ground breaking, merely expecting the software we pay for to at least be 'current'. As far as I can tell, Corona no longer has a USP or any redeeming feature to keep me from switching back to Vray or moving over to FStorm or some other render engine. Tech is a fast moving space, so if your customers are disappointed or leaving, you can only survive off loyalty for so long imo. If you can't keep up, you get left behind, it's that simple.