LogFAQs > #979303092

It's very doable to complete the Pokedex in the newer games, but YMMV on if that's considered "rewarding" to you as a player because, for the most part, the actual reward(s) usually aren't.

The lone exception might be Legends Arceus because it's a requirement to actually battle and catch Arceus itself.This is probably the easiest game to catch everything in too, possibly because of that, and without ever needing to go online too. No version exclusives, rarer Pokemon show up in these random warp events, and evolutionary items have been added to replace trade evolution requirements. That said, catching all the Pokemon here doesn't technically count as completing the dex as now there are research levels for every creature: these consist of using certain moves, battling with that Pokemon a certain amount of times, catching that Pokemon a certain amount of times, and so on.

For mainline titles, starting with SM, they neutered the dex so that it only consists of Pokemon in those games/regions, making it a lot easier to complete. You still have to jump through all the usual hoops to do it, just not as much, but generally you're able to complete like 80% of the dex without needing online/trading. Also, if you're willing to do a little research and don't care about legality, the Switch games have tons of Pokemon generators out there.

HG is probably the last game I really put my nose to the grindstone to complete, kind of like what you're experiencing now.