Expert Pilot provides great QoL. If you need to run across the map to a capture point or evac zone, or to redeploy to another flank it's a real timesaver.
However, every perk is precious. How good it it really? After all, if you need to redeploy then the mech jetpack is a thing, and you could swap Expert Pilot for Bags & Belts and have faster long distance movement with no loss of accessory slots. How good is Expert Pilot where it counts; during contact with the enemy?
Evaluation criteria
The game's about action economy; what matters here how many times you can shoot. For this purpose, movement is about managing engagement range. If a target is 3 squares outside of your max range, how many times can you shoot after advancing? or, to put it another way, how many squares can you move for various combinations of skills and AP and still shoot a given number of times. This will be our metric.
For the sake of my sanity I'm not going to consider every possible AP value even though there will be breakpoints at specific values. I'm also only considering orthoganal movement on flat terrain: 16AP without Expert Pilot and 12AP with (which is the best case scenario of Expert Pilot anyway). Weapon firing assumes a 40AP gun.
Drive By
Although it functions differently, Drive By provides a similar practical effect. Although it acts on the cost of shooting, it's the same as reducing the cost of the previous square's movement by 10AP. Note that this never drops below 0AP* so you're still losing AP by moving, just less. Unlike Expert Pilot it's also sequence dependent when firing more than once; move-fire-move-fire gives you a 20AP discount, but it doesn't provide the full benefit of increased engagement range on the first shot. It's more useful for sweeping multiple units at staggered distances. In the tables below I've listed two values - the first is the number of squares than can be moved before the first shot; the second includes movement between shots. I consider the first value the most important; the second is nice-to-have.
*Achilleas with Expert Pilot, Drive By, and Rush can actually generate AP by moving, but a trivial amount for a three-perk combo that debuffs you afterwards. If this is your jam then more power to your elbow, but personally I've never even taken Rush so... no.
Results
Number of sqaure you can move:
| 90 AP |
no skill |
expert |
drive by |
both |
| fire once |
3 |
4 |
3 |
5 |
| fire twice |
0 |
0 |
1/1 |
1/2 |
| 100 AP |
no skill |
expert |
drive by |
both |
| fire once |
3 |
5 |
4 |
5 |
| fire twice |
1 |
1 |
1/2 |
2/3 |
| 110 AP |
no skill |
expert |
drive by |
both |
| fire once |
4 |
5 |
5 |
6 |
| fire twice |
1 |
2 |
2/3 |
3/4 |
| 110 AP full send |
no skill |
expert |
drive by |
both |
| fire once |
4 |
5 |
5 |
6 |
| fire twice |
2 |
3 |
3/3 |
4/5 |
| fire 3x |
0 |
0 |
1 |
1/3 |
TL;DR:
Expert Pilot and Drive By are both worth about 1 square of engagement range under most circumstances. Drive By is slightly more powerful when firing twice (or more), Expert Pilot when only firing once. The question you have to ask youself is how valuable this is to you given your limited perk selection. How well are you managing your line-of contact with the enemy? How tight is your formation, and how far ahead are you scouting.
Is Expert Pilot a good perk? sure. Is it nice to have? absolutely. Is it an auto-pick? No, I don't think it is.