Decker is superficially similar to HyperCard because it's primarily 1-bit, but it's different enough to require a totally new learning curve. It's quite difficult to use, requires learning "Lil" a new and unique language, and is missing many HyperCard/MacPaint affordances you might be looking for if you're expecting HyperCard.
The upshot is that HyperCard artists can't switch and continue to use HyperCard in a browser thanks to Infinite Mac.
It's not. There's isn't a single most important thing. HyperCard was an almost perfect blend of many things. That's why it's easy to spot when they're missing, like some omissions or differences in Decker.
The upshot is that HyperCard artists can't switch and continue to use HyperCard in a browser thanks to Infinite Mac.
So close, yet so far.
Similar, but different.