Honestly a lot of ME background material makes no sense when put against main plot points; in ME people see garden worlds as these precious resources, but one of the random planets mentions that a local corp literally mined it down to the core and made it an asteroid, an Asari university build a particle accelerator that rings an entire planet. Their industrial capacity is beyond insane. The Quarians should all be living on O'Neill cylinders by now, not worrying about the migrant fleet. Every single of them carries an omnitool which can be used to build parts to build bigger 3-D printers.
There shouldn't be an issue with ships, they should be able to just build ships from random asteroid belts they're mining when they float through systems. You could excuse it by saying they're scared of the Geth, but that still doesn't make sense; the Quarians were an established space faring race, even if the Geth took every world they had and closed the borders they should have still brought enough industrial capability, capital and people to have rebuilt into an actual space faring species.
Fuck me the Andromeda initiative was a privately funded venture that built multiple dreadnought sized vessels and a functional city in space. But the Quarians are all doomed to live on cramped, second hand ships? No space stations? The Migrant fleet should have realistically found some Terminus system, said 'this is ours now' mined the fuck out of it and build a load of habitats. The Terminus warlords would have went 'fair enough' when faced with the choice of engaging the single largest fleet in being in the galaxy and that would have been it.
You could still do the 'waaah woe is me!' thing with them flitting around the galaxy on pilgrimages, but also have had the Quarians not behave like utter retards. Hell, that goes for most other races as well, the Terminus regions and outlying council regions should be filled with asteroid habitats, O neill cylinders, Power satellite swarms, and other megaengineering structures. Their equivalent to millionaires can fund extragalactic colony efforts and the Illusive Man had a fleet, the logistics to supply it and somehow entire worlds at his beck and call. The ability for the ME species to build is staggering; and it makes the given fleet numbers, and state of the world make zero sense.