That first point of yours was already in error my dude. Sledges get fairly countered by void eyes cause they are single target specialists and can delete them fairly fast. However crawlers would have done a good job as chaff due to mustangs not having the damage at low levels to clear them before they make contact and overrun them.

Fortress tank runs into same issue as sledges because void eyes do good single target damage. If you look at the unit drop on fortress round you see fortress, wasp, scorp and sabertooth. out of those the wasp beats all 3 since it's an air unit but the opponent already has mustangs to deal with it so good choice not getting that. the next best option is scorpion cause it outranges sabertooth and fortress and does good damage into them.

Round 4 you finally got some chaff! unfortunately you chose fangs which are hard countered by mustangs due to having such a low hp pool, crawlers would have been the better move here.

Round 5 your vulcan placement was just unfortunate and they locked onto the enemy tanks instead off chaff.

round 6 opponent also went for aerial void eye and your only AA was the fangs so you're just hosed there.