That seems to be true. Some enhancements of the game were cool, even though I don't use wings and play solo. I never used fighters either, yet.
But it seems to me that all such expansions are possible because they just grow naturally out of the core game. That is, you fly in a boat and see a cockpit. You can enter into an SRV. So, all you have to code is a way to get into a fighter, which is based on existing code.
To me that is not an expansion but an enhancement, no smarter than a reskin as they do in shooter games. No expansion was launched. We've seen gfx updates and that is nice. Engineers adds nothing substantial in that they are just missions, so they are based on existing code to get something and deliver, or donate to an engineer. The rest is some interface and a RNG, which is trivial for a team like FD. There are some parameters to be set in code, a sto what ranges the randomness will be allowed to affect.
More ships is also based on existing code. This is just gfx artist conveyor belt work.
An expansion of a game means loads of new code that actually increases the possibilities of the game engine and functions. So space legs might be that in that it opens up whole new areas to explore. New types of gameplay, as people suggest, boarding parties and defense of ships etc.
But every game (engine) has built-in limitations. We have an advanced flight model but who actually flies without flight assist? Stacked on top were missions. Maybe that has its own 'engine' of sorts, but it doesn't truly connect to the flight model engine. What you code is equally what it allows and what it won't.
And so you have the problem of thinking up new stuff but are confined to the preset course of what you already coded. You are in a rut. So you can make chained and more complex missions out of the mission system. You can add more ships through the existing ship creation procedures. You can reskin and sell it as fluff so people can have pink engine flames. You can add engineers based on the mission system and tweak in some extra code where required.
Get out of the rut means to enhance the game engine, causing bug fests. So whatever they do will be a stack on top of what is there but not too deeply inserted in or merged with the core engine. That is what RSI did, code a game engine and realize they needed more and had to redo the bloody thing, which must have cost them a year or more of our lives.
Fluff is easy and keeps some percentage of the player base happy ranging from delight to meh. Substantial additions take time and so there is the fight between appeasing the masses with fluff or small enhancements and the time it takes to actually produce something really big. If it takes too long, people leave. If you don't produce anything really big, people leave. If your balance between fluff and substantial isn't addressing the need of the masses + calculated loss in playerbase (because you cannot appease everyone, all the time) is off, your investors moan.
In a sense and in essence, a developer cannot ever do it right. Because design approach to modern gaming means you get the core game out and then hope its awesome enough to attract naturally inclined fanboys to carry you over to expansion before the investors moan and retreat. That is why we still have a game I feel is a bare-boned game. Fanatics run through the engineers in no time, dedicated players will muster up tools and spreadsheets to help the hapless. And so the players catch up to what is in the pipeline putting more pressure on FD.
Another example of this is Star Trek Online. They release literally half seasons (like 13.55) and have repeatable missions for 3 weeks to keep people in doing at least something, boring as it is because they are in a rut without the time do make proper expansions, so they reskin and repeat based on existing game mechanics. As long as they can show numbers of people in the game to investors, it is all good.
So I expect FD to keep doing these rather meager updates because to actually enhance the game means years of coding and many months of testing and bug hunting, leading to annoyed players. It is like that varieté thing where a guy puts spinning plates on poles and has to run back and forth spinning them up again before they crash to the ground. And how many can he keep going?