I reckon Coach will recommend using heart rate in addition to power, if you go with a powermeter. No argument from me there — both are useful info.
That said, I’m a long-term convert to power. I started using a Powertap hub-based wheel back in the early 2000s when they first came on the market. Today, I’m using a Power2Max crankset (https://power2max.cc/), which has really been trouble-free.
To me, the benefits of using power include: more data that allows me to measure/maintain workouts at prescribed levels (both on the road and on a trainer); information that helps me gauge efforts (especially at races) so that I don’t push too hard (up hills and at the start of the bike are places I tend to do this) or to keep my level of effort up (long, flat races I’ve found I tend to zone out and can let my level of effort drop); unbiased info that helps me know if weather/temp/emotions are affecting my ride (i.e., I might feel really great, but my power levels are higher than planned, so I might want to back it off a bit); and instant feedback on level of effort (especially useful on short hills). note: I usually set my computer to show a rolling 3 second or more average power number to smooth out the jumps/spikes in power that naturally occur in shorter periods of time.
I’ve also found that using power all the time can really help me understand my race thresholds better than I do with a straight-up threshold test. As an example, reviewing power data after a half Ironman race gives me a really good data point on what I can maintain for 2+ hours (and then translate that to a 5+ hour IM ride) — far better than the estimate I’ve been able to get from a 20 min power test on a trainer/road.
If you’re not into data/numbers, you might not like power as much as I do — but I’ve found it to be a much more consistent, usable data set than anything else I’ve used.