A few thoughts:
1) There's strategic blobbing: all your available mobile forces being involved in the same fleet action.
2) Then there's tactical blobbing: all your available mobile forces
on one planet (regardless of what percent of your overall force that represents) being all in one location.
3) Neither form of blobbing is the end of the world if it's a really common thing. It's one of those things we try to poke holes in game-design wise because it seems like it's an area where the player could be challenged to think a lot more. But, like the whole "battlefields within battlefields" idea, we understand that a ton of the other design decisions made (ship speeds, ship ranges, very few things that can block movement, etc) may simply limit what can really be done about it. Blobbing being so good probably does make the game less fun than it could be, but the kinds of changes necessary to fundamentally change the situation may cause more loss of fun than gain. AI Eyes are an example of something that does counter-blob but really annoys a lot of players (largely due to how common they are and how low-variety they were, we're still working on that).
3) Strategic blobbing is probably always optimal when you can pull it off. But structuring things so that you can pull it off is often (in a challenging scenario) a highly non-trivial problem that does involve significant thought and falls prey to a variety of non-predictable factors. And there are the Eyes which highly incentivize not just doing it blindly
everywhere.
4) Tactical blobbing is definitely not
optimal in nearly any non-trivial engagement.
- I know this because of several past community members going into great detail about microing the positions of their fighters, bombers, and frigates (and other stuff, but the triangle being the most obvious) to minimize the chance of their ships taking fire from the nemesis type. The difference that could make in a battle's outcome was pretty stark.
- There's also various AoE-damage considerations.
- And tons of tactics where sneaking forces up under cloaker starship cover or pulling parts of forces back to keep them out of enemy fire (bombards, enclaves) or having a decoy force to pull enemy attention (transports, riots)
- And, of course, fortresses, though that's already been pointed out as the counter to tactical blobbing. Honestly the whole "can't even hurt bombers" thing doesn't really sit well with me but I don't want to mess with it out of mere personal dislike
- Grav Drains / Grav Guardians are one situation I can think of where you'd want to only send in your grav-immune or "I don't care if this dies" ships to assassinate them, and a situation where if your fleet is in multiple pieces it will be less likely to all get caught in the quicksand.
- And I could go on with various reasons for moving your ships-on-planet around in multiple distinct groups.
5) That said, tactical blobbing is also very often effective
enough that there's no
need to do lots of micro. Not optimal, but good enough. Also, the principle of concentrating all your force at the current critical point of the battle is a massive point in favor of tactical blobbing: getting fancy with micro can give you various advantages but unless you're pretty good at it you'll probably lose out in net terms due to unfocused (or, worse, unused) DPS.
6) For now, changes for the purpose of reducing the optimality of blobbing are not really in the offing. I keep thinking about it, and I can think of a few things that might work if seeded on at-most-one planet in each entire galaxy (e.g. a four-unit set spread out across a planet where each gets 2x as strong with each other piece that is dead, making you choose between splitting your forces into four or suffer the firepower of the last one at 8x power), but in general this is an area to tread carefully. Blobbing is often a-fun, but it's not anti-fun.