I try and pick apps based on package size the rare time I look for some app. There are still apps out there made like they were 10 years ago (that probably haven't been updated in 10 years) where the package size is sub 10mb, sometimes sub 1mb. You get an app like that it is performant and will fly on any iphone really, and barely impact battery life in all likelihood.
Package size has very low correlation to launch time. The binary and assets are separate. Additionally some slow app launches are simply waiting for a network request or chain before the view controller renders.
Situational. But often these apps are doing something just using that standard ios ux library from the really old days, and they open almost instantly as a result as it was designed to work on an iphone 3gs.
In theory, sure, but in practice devs who care about package size correlate to those who care about launch times.