Good gravy, this is absolutely nail-biting stuff! 5e really seems to do these combats well - or you do!
If I tried this in 3.5 half the enemy couldn't touch the PCs and the big bads would be either punch bags or too strong. Very well played, sir!
In truth a lot of the little bad guys didn't do much but get in the way, and make the guys make choices- and soak up all the Union's spells/powers/resources. That said I mod all the bad guys, just a touch, so that have a little more oomph. The players get a little panicked (almost always) when a host of little bad guys start filtering around the front line (sometimes taking hits to get there) and making it through to the squishier members of the group. When this happens the players usually start 'telling' each other what they should do, 'for the best', I love it when this happens- the threat perceived is (most times) greater than the actual threat.
Thanks for reading, and commenting, it is very much appreciated.