Just limit the number of reps a ship can accept at any one time. This makes the blob useless for remaining alive - which is the major issue right now.
Smaller groups could take more losses but still win on attrition - if they build their own stuff. This stops things being a completely one sided affair.
People will always group up as big as they can get, human nature.
Great idea, but this means bigger ships which could sport better resists would be the meta for fleet battles, which feels kind of stagnant, but this would mean nullsec blobs not too overpowered!
It is better to create change by incentives than by limits. A great many things can be achieved by cleverly designed game mechanics, but there aren’t that many skilled designers available to do so, and certainly none of them are currently designing for CPP/EvE.
You could create a mechanic whereby corps derive certain benefits from having member counts (thereby encouraging people to join and expand corps). And then limit those benefits by some variation of “average activity/productivity” stats for the corp, so the corps are encouraged to manage their membership to encourage interaction with the game rather than simply padding it with alts.
You mention “diseconomies of scale” and that’s a good point; as you say currently there’s no real downside to “bigger is better”. On the other hand the choice should be a choice, with pros and cons either way - not just a “here’s the size limit” or a “biggest is best” choice. Management costs for running corps and alliances could be figured in so that corps have a reason to choose the most efficient size and level of membership activity for their goals. It would also provide various sinks.
At any rate, “woulda coulda shoulda” discussions for the proper design of EVE are mostly here for our own entertainment. From all evidence they have absolutely zero impact on anyone at CCP so I guess the best response is to enjoy what CCP provides if you can, walk away if you can’t, and consider forum discussions to be just a way to pass the time with your fellow players.
Like it - seeing some intelligent ideas to dealing with N plus 1 and maybe more fleet diversity. It might mean we don’t see the massive battles that EVE gets PR off, but we might see more interesting battles with better gameplay,