This. I use TrainingPeaks with Intervals as well as Strava - well, and Garmin Connect and Zwift and ...

Intervals - as well as TP, TR, Zwift, Garmin Connect, and Strava, are pretty lightweight on the free side (let's face it, you get a lot for free) and they are all integrated to some extent (push/pull varies by app).

I also advocate for supporting David (Intervals) with a $12 every 3-month commitment. It's an incredible resource.

Woah this looks cool! I use a chrome extension (elevate for Strava) that gives you lots of additional stats but this seems to have even more.

intervals.icu is fabulous and 100% worth paying to support the single dev who runs it.

Elevate is no longer developed as a browser extension and lives on as a desktop app: https://github.com/thomaschampagne/elevate/

and also: https://runalyze.com

Also gets data from Strava (and so much more, mostly free).