I’m another one who lives in extreme heat and has learned the hard way that HR signals long before RPE does. Going by RPE, I’ll feel fine almost right up to the moment when everything goes to absolute hell. If I keep an eye on HR, I can back off and keep the crash from happening.
Calling out that it’s mostly in heat where this is valuable is key, at least for me. In the winter, RPE is a much better signal…again, for me.
For me heat exhaustion comes on rapidly without warning - scary rapid. Body says “you’re stopping this sh_t right now!” 
and gives me a feeling of nausea that stays a while. If it wasn’t so rapid, I could use RPE to keep it at bay, but I don’t want to be put in “time out” so I use the HRM to keep me well clear of that condition. Another thing about RPE. Let’s not pretend RPE is always “truthful” of the stress your body is experiencing. What happens when a surge of adrenaline pumps through your veins so you can fight that saber tooth, or impress that potential reproduction mate?
You are not.
Point of order: he could be. Just not for this reason.
Carry on.
But you don’t need HR to hold yourself back - just target a lower power during and/or perceived exertion during and after.
PPP: If you know your power, then at best heart rate is redundant, but at worst it is misleading.
PPP: If it feels hard, it is hard.
Piss poor planning?
Puff puff pass?
Paycheck protection program?
Public private partnership?
Pithy Power Proverb
Thank you sir!
RPE changes w/ my psychological state (depression/anxiety - high RPE, excitement/competitiveness - low RPE). How many times have you seen race cyclists get in a wreck and immediately get back on the bike - only to get off minutes later w/ broken bones, etc. How reliable was the RPE system then? Ever wonder why football players get them selves “pumped up/excited” before a play?
By using HR cap as balancing point, power itself becomes moving target:
For me personally, RPE is actually the worst ruler: Z3+ are pretty spot on but below that I would end up around 70% of FTP (and it feels good). But I know from experience that with my volume this is not sustainable in long term.
Good point. I’ve been off the bike for about a week (sore knee) and today I went on a easy Z2 ride in Florida heat. My heart rate was significantly higher. Was this due to aerobic detraining in a week? Of course not - it was from loss of heat adaptation. Living in Florida I notice this a lot. I expect to be back to normal in 1/2 weeks.
That’s true, where I live, weather is much more tolerable, nice steady 20-25C dry temperature i.e. I can trust more HR not changing too much due external factors.
Oh ya! I don’t think you’re a "big…deep breaths
Sounds to me like The_Cog needs to switch gears 
I have two use cases for HR data on the bike.
Riding without power (only my road bike and smart trainer have power, but that’s only 50% of my total riding).
RPE vs power vs HR on a bad day. Say I’m doing a threshold block, and can’t maintain power. If my HR is higher than expected, I’m probably sick/stressed/tired. RPE could do this, but I like having the validation that something is wrong beyond my brain telling me “this is hard”.
In intervals.icu you can compare HR @ Power on specific dates. There is so much info out there I’m sure I’m not using all of it but that one caught my eye and it was nice to compare not only power and speed between two events that were months apart but it was great to see a lower HR across the board for all of it after months of training over the winter and this spring.
I see HR as a proxy for RPE and vice versa.
I don’t have HR on the main screens of my bike computer but I can look at my watch if I’m curious but I can generally guess what it is while doing steady efforts, it’s the up and down stuff where it can get a bit fuzzy.
Pretentious Prosaic Posturing?
While they both increase with increasing exercise intensity, HR is generally linear, whereas PE is non-linear.
More importantly, PE accounts for all inputs to that part of the brain, whereas a HR only tells you how fast your heart is beating.