I don’t think Typescript knowledge (or use) is really necessary to write Obsidian plugins. You can just write plain Javascript using ES2018 features (such as classes, generators, and async functions), which are available in most browsers as well as Electron.
If you code directly in JS and CSS in a subdirectory of your plugins folder, you don’t need node, npm, rollup, typescript, or really any of that stuff. The main difference from the example code is that instead of writing import {...whatever} from "obsidian"; you write {...whatever} = require("obsidian");, and leave out any type declarations/casts. That’s pretty much it.
Of course, while doing development, you may need to reload your plugin after making changes. You can do this by reloading, sure, but it’s easier to just go to settings and then toggle the plugin off, then back on again
You can also automate this process from within the plugin itself, by including a command that does something like this:
const id = this.manifest.id, plugins = this.app.plugins;
plugins.disablePlugin(id).then(() => plugins.enablePlugin(id));
This will reload the plugin from disk and run the new version’s onload(), after first calling the old version’s onunload(). It’s basically the same as going into the settings and toggling the plugin off and back on again.
The main downside to not using Typescript and rollup is that you can’t use any node modules in your plugin without copying and pasting. For the plugins I’ve been developing so far, this is not really an obstacle, though.
I am somewhat curious as to why the Obsidian devs are using an ES5 target in the sample plugin, though, as it means that many Typescript features will be emulated in Javascript rather than using the V8 native versions: notably classes and async functions are emulated when using an ES5 target.
(It’s possible that Obsidian itself is being built with such emulation in order to enable Typescript features that don’t work with ES2015+, such as decorators. But ISTM that wouldn’t be a reason for plugins to do that sort of emulation, too.)