Bad assumption. There are climbs that are 20-25% grade or more that I would be glad to have a 50t for if I was regularly spending time on them.
Mechanical advantage comes from a larger front chainring which causes less chain curl and a lack of cross chaining for the middle of the cassette and is roughly 1-3w depending on how much power you are putting out.
Gear yourself for usable range. Generally speaking there is no reason to upsize your front chainring unless you are really looking for marginal gains.
(begin the part where I don’t follow my own advice)
I run a 36t with a 10-45t because I want a tighter ratio and I was literally never using the 50t. I really disliked the jumps on the Shimano 10-51 but I’m keeping it as a backup for super steep days.