I don't think it's the actual file sizes that people object to so much as all the redundancy and inefficiency that the bloat is indicative of. That is, for every increase in CPU, storage, and bandwidth; app developers insist on throwing it away with another layer of frameworks and intermediary libraries.
What Moore's Law giveth, React/Flutter taketh away...
There are smaller/faster ready like libraries such as preact and inferno btw. React does offer a lot of advantages though mostly for diagnostic purposes for developers.
What Moore's Law giveth, React/Flutter taketh away...