I did the same with an MBA, replacing its battery in less than an hour by virtue of the battery not being glued to the case, nor having to worry about hidden clips built into the case, nor having to carefully dig out the guts of the system and putting them back together.
The MBP is in a totally different class -- as iFixit shows, you don't start removing the battery until step 51! And they're not kidding: to get to the battery, you have to do things like remove the trackpad assembly and pry out the logic board assembly.
Sure, you can amortize the 1-3 hours of labor over years of device ownership, but at every step, you're dealing with delicate parts, putting you in danger of turning your expensive, trusty daily driver into a brick.
Batteries are a wear item, guaranteed to have to be replaced. Apple's managers, designers, and engineers could show more empathy for their customers by making it easier and less risky to replace their wear items.