Honestly, I'd buff weavewalk to 2 fragment slots. For weavers call, I'd add, threadlings unravel targets and a third fragment slot. This would make a swarmers rework necessary. Which I think a good rework would be "destroying tangles spawns 2 threadlings and dealing damage to unraveled targets occasionally spawn threadlings (horde shuttle)"

Adding Horde Shuttle to Swarmers is a great idea, but I think it would be better to keep the Unravel effect on them too, so it's all in one. Having the Exotic provide the loop of: make Threadling > Unravel enemy > make Threadling and so on would make it fairly self-sufficient. No arguments with adding a second fragment slot to Weavewalk. For Weaver's Call, I could see it getting a third slot or an extra effect, but not both. If I had to choose between them, I'd prefer an extra effect - maybe a Weavewalk buff would mitigate it, but something involving Sever or Woven Mail would be great. The only in-subclass way that Broodweaver can use those keywords are Threads of Warding and Isolation, which leave it lacking in the defence department.

Weaver's Call is probably the most deserving of 3, in addition to some other buffs. Mostly because you're 100% going to pick Evolution if you're picking Weaver's