I think the point you're missing is that Flash supported an entire ecosystem. Because it was easy to distribute the files (and steal them from other portals), there were tons of game portals out there competing for traffic. This competition created incentives to do special deals (add my logo and a link for $2k before you launch). I released several games sponsored by Kongregate which went viral and got distributed to thousands of portals. Higher-tier portals would reach out and purchase a site-locked version without their competitor's branding for an additional $300-$1k depending on if they had their own API for high scores and such. Because there were SO many portals, it wasn't as winner-take-all as the modern mobile marketplaces.

I could easily recreate my games in javascript today (or swift. or C#/unity. or whatever) from an "is this possible" point of view, but I think it's much harder to make money today. You could argue that's more due to the competition level and number of creators than Flash, but I think the siloed app stores are awful for the long tail and smaller developers.

That ramp-up of competition kind of happened even before Flash was dead-dead, though--the big portals existed in a time before Facebook games (which suck now but were amazing for awhile) and mobile games. It's wild now to see my kids (5 & 8) play a lot of online games on modern much-shittier-than-Kongregate-and-Newgrounds portals, but there's basically a short time period between "old enough to play games" and "old enough for their own phone or steam account" that they're in right now, and I suspect that audience isn't big enough to support the kind of innovation we saw before Facebook games (which were also made with Flash, for the most part!).