The Devs have said that Imperials get more ship abilities, to balance their relative lack of upgrade slots, and unique upgrade type. Let's examine how have they done that.
I'm going to look at all the ships in the conversion kits, and check their access to "special" abilities via some extra cards, like titles and configurations, or native ship abilities. If it is truly to compensate the imperials for the lack of slots, they should have a massive advantage in this field. I made a few assumptions where we don't know for sure. I don't know if the Kimogila gets the Enforcer title, I assumed not. On the other hand, I'm not sure if the Scyk counts as a ship ability, so its fine.
Rebel ships without titles, configurations and ship abilities:
HWK - Title
K-Wing - Nothing
T-65 - Configuration
E-Wing - Ship ability
U-Wing - Configuration
YT-2400 - Ship ability, Title
Modified YT - Title
A-Wing - Ship ability
Wookiee ship - Nothing
ARC - Nothing
B-Wing - Nothing
Z-95 - Nothing
Y-Wing - Nothing
TIE Fighter - Nothing
VCX - Title, Ship Ability
Phantom I - Title, Ship ability
Phantom II - Title, Ship ability
7/17
Scum ships without titles, configurations and ship abilities
Quadjumper - Ship ability
Aggressor - Title, Ship ability
Starviper - Title, Ship ability
Firespray - Titles
M3A - Ship ability (?)
Jumpmaster - Title
YV-666 - Title
Z-95 - Nothing
Y-Wing - Nothing
Scurrg - Title
Fangfighter - Ship ability
Khiraxz - Nothing (probably?)
G1-A - Title
Kimogilla - Ship ability
Lancer - Title (probably?)
HWK - Title
3/16
Imperial ships without titles, configurations and ship abilities
Reaper - Ship ability
Advanced - Ship ability
TIE fighter - Nothing
Gunboat - Configurations
Defender - Ship ability
Lambda - Title
TAP - Nothing
Aggressor - Nothing
Striker - Ship ability
Punisher - Nothing
Decimator - Title (probably?)
Phantom - Ship ability
Interceptor - Ship ability
Bomber - Ship ability
4/14
So, on one hand, percentage wise, yeah, the rebels have it the worst. They have the most ship without special abilities, but they also have the most ships (I didn't count Lando's falcon yet).... But they also have the same number of ships WITH special abilities as the Empire. The TIE fighter doesn't have a title for rebels anymore, but it stands to reason that it is because now included in ALL rebel TIEs, included in their price. (The rebels still have better TIES).
Scum really blows it out of the sky. They seemingly have the most, sometimes multiple sources of additional abilities on the same ship, but some of them are quite rubbish, and some are unconfirmed. Still, they do have a lot.
Now, don't forget, Rebels and Scum still have access to more unique crew (all of the revealed named gunners are quite good, all are rebels and scum... it is also very unlikely we get an imperial unique gunner), illicit upgrades and astromechs, in addition to their ship abilities, titles and configurations.
I don't see how is this supposed to "balance" out, if FFG isn't making an effort to distribute ship abilities carefully.
BEFORE YOU START TYPING: "But Kaine, Titles and configurations aren't the same as ship abilities"... Yes they are. They increase the number of abilities a ship has access to. They provide potential synergy. More synergy, more power.