How can I efficiently use Web apps on my Mac?
In general, this is an inherent flaw in all web apps, even the good ones and a fatal flaw in poorly designed web apps or web apps where your needs aren’t the main design goal. 

You will want to shift your work to apps that can run native if efficiency is required. Offline and API access is generally far more efficient as you can work asyncronously or disconnected which decouples your interaction from the server code and processing with all network delays adding to your frustration. 

Also, be sure you try browsers like safari that sharply curtail resource usage when off screen, background and minimized. Perhaps your browser can help with the 20 second startup delays and even that shouldn’t be a huge drain if you get proper work done once the app is runnning. 

Lastly, a native app can be coded as a web app and still cause you grief. Some notable ones I've come across are the Atom editor, Slack app and other electron or node or react based apps that are glorified web view containers.

Here's a very well thought out article from some very smart and well funded engineers on balancing the decision to build a pure native app (or building several iterations of the same app as your team learns how to engineer and expand the app) vs building a common core that will run across platforms or embed a web view.


Growing Pains: Migrating Slack’s Desktop App to BrowserView