yes, pushing the limits will definitely increase the body's resilience and that is why you are so fast for so long whereas a guy like me that has been involved almost exclusively with weights for decades is not fast and has low endurance. Since one of my objectives is to lose another 5kg so that running is actually more efficient, knowing that I don't have to really push myself which results in me dreading the exercise, this is a nice little trick to know though.
Your stairs tactic is a good one, and one that other people should also use.
Losing weight just seems to be hard generally, hence the massive industry serving that market. I really feel I'm lucky to not struggle on that front, but I was putting on weight before I started running and that was one incentive to get out there. I do like my food, so have to get the balance right.
I don't think losing weight is hard, it just takes a long time and that is why most people give up. They expect immediate results and things just don't work that way.
The only really quick way is to chop bits off 😁