Thunderbird usability

I tried fight moving my thunderbirds into a shield ball, but it didn't attack and got killed by felons, which makes me wonder.

1. Why is thunderbird perma set to hold fire, even when I set it to fire at will and fight move, it still never attacks unless explicitly ordered with force fire command

2. Why is felon able to hit thunderbird so easily? I'm already put off that ravens are essentially useless against felons because they have to dive bomb them, but thunderbird is supposed to be the shield ball counter...

Shieldball is the ultimate form of snowballing in the game. The more it grows, the harder it is to stop. Enough shields will block incoming damage unless they over power the shield strength and Outlaws are able to reveal most common unit stack counters like cloaked Snitches. Felon on the other hand is able to snipe snitch drops from air or wreck Thunderbirds from air.

An enormous shield ball is only stopped by Shockley or Reef Disarm missile due to penetrating shields and disabling huge amount of stacked units. Other options are draining the shields to let high damage attacks like Licho or Bertha bombardment penetrate the shields and wipe the ball before Felons or other form of AA manages to intercept them (applies only to Lichos).

You could catch moment when sb drained, or use more tb and licho/phoenixes then.
Felon best aa in game, he easy killing lichos and any other air if he have enough power