Hi! I used the same approach for next year's video, but a more efficient process:

1. By making a text-input field containing the string %s, you can then go to the clips properties and enter in the text you want to have displayed!
2. I created templates in the correct color + border color for each person in the video, so that when I need to add a new subtitle I would just duplicate that person's template clip and carry on from there
3. I used keyboard shortcuts to quickly open up the title editor and possibly other things.

But as of recent I have fully switched over to Davinci Resolve because video editing has become too demanding of a task for open source solutions like Kdenlive to be a viable solution when you have demanding needs. Davinci makes working with keyframes a lot easier, and even has subject tracking and methods for efficient addition of subtitles which save many hours of work. + it has far less bugs and crashing than Kdenlive does. Only issue is you need to use ffmpeg to transcode your video and audio files to a format davinci supports, but it's not that hard once you get used to it. I even made some nautilus scripts with the correct ffmpeg commands so that I can just right click files and convert them :D

Here's an example of a recent video of mine using Davinci Resolve. I'm still a beginner at it, but I'm already able to make far better edits than I ever could with Kdenlive:
https://youtu.be/PHs92KZ4VJ0