First, the conversation is about medical supplies.
Second, the Quarians would be starting from scratch IF they succeeded and took Rannoch. They'd be in a similar position in some other location, but in Turian jurisdiction, the Turians would be nearby to lend support, if not material then at least logistical. And the Quarians could do to them same. This conversation is not evidence the Quarians should have attacked Rannoch, it is the opposite.
By all appearances, the Turians would be drawing on the Quarians' resources, not the other way around. They accept the assistance of the Quarian fleet, but they don't reciprocate in any way I've seen (Councilor Irissa snarks about them as "the vagrants" immediately following the
Rannoch arc). What makes you think they'd be able, let alone willing, to help the Quarians settle in when they're already stretched thin and asking others for assistance with logistics? At best, the "suit rats" would be a secondary priority for medicine, protection, food etc. At worst, they'd be stripped and abandoned at the first opportunity.
They're self-sufficient on
Rannoch - they wouldn't produce a surplus, but they're expected to meet nobody's needs but their own, and they succeed at this. The Quarians expect to cannibalize a good deal of their fleet in the process of resettling on
Rannoch (per Tali in ME2), but it leaves plenty of ships left over to aid the wider war effort. I'd expect the food processing gear to be offloaded from the liveships, leaving behind bulky glass cannons which were otherwise cored out. IIRC we only see two in the ending cutscene, though. As we're told in ME3 if the Geth are destroyed, they're roughing it in the beginning, but they make it.