OP, as noted by many, there must be some diff. in your weight to the guyz you're comparing with.
Power relative to what is being lifted.
as Trakhak noted, starting in the front and slowly drifting back through the group is a long used plan to get thru climbs where you're 'close', but not quite at the level of those you're with.
As for HR, yes, it can vary for each individual over the range of effort; but ultimately once in the higher reaches, HR levels and limits are fairly equal.
Once in the mid-high 170's and 180s' the vast majority of 'fit' cyclists are redlining... age , fitness, efficiency all to be considered.
There are so many things which impact watts/kg, including and very important, is how well/much O2, your VO2, you can process is a key indicator.
https://theconversation.com/the-scie...-12-to-21-2063
A lot of these indicators can only be reasonably measured in-lab, and are at best, estimates from other markers.
IE - I would do on-road AT tests 3-4 times a year, and vary the test method to make sure I wasn't mindset into 'method' and outcome.
A 1X testing of AT/LT is really not worth much...
lotta good comments from all on things to consider.
how fast you go up any hill, depends on what you can do to maximize advantages and minimize loses.
you know the 'rides' on which all this transpires... why not get out there and try different approaches to 'riding' those sections?
170 lbers can be good climbers, they're just gonna work quite a bit harder...
Ride On
Yuri