Its quite frustrating to see how everything is turning out to be (a cluster f*** of unit design) especially when you see how the design has evolved from its predecessor.
In BW, factory units consisted of the vulture, tank and goliath. The vulture would be the fast unit which occupied several key roles like being meatshields for the tanks, zoning space via mini nukes and harass. The tank is the core ground firepower for the mech army but is very immobile. Goliaths provide the essential AA (instead of having to get air units) and were easily accessible. The beautiful thing about these three units was that the factory could stand on its own and depending on the enemy composition, all one had to do was adjust the ratio of the 3 as the game went along.
In HOTS, we get widow mines, hellions, tanks and thors. Widow mines overlap with siege tanks plus they also hit air. Hellions while being able to harass and be meatshields ala hellbats don't quite zone space (spider mines imo was one of the most important pieces for an mech army as it covered up immobility weakness). Siege tanks don't have enough firepower yet they cost more and take up more supply (plus a million hard counters). Thors are too clumsy and mineral intensive to provide a solid AA option requiring need for starport units ala viking. Unlike its predecessor the factory units NEED the support from starport based units. One cannot just adjust the ratio between the 4 to take on different type of enemy composition. Needless to say, the factory units here act better as support units.
Now in LOTV, we get two more additional units in the form of the liberator and cyclones. Liberators are literally a flying thor with siege mode for AtG. Cyclones on the other hand I have no idea what role they are trying to fill (Plus the lock on ability just doesnt fit in the world of SC). What are the purpose of these two units? Why not just take out the siege tank and have the liberator only because the way I see it, they've combined two units that somewhat get rid of each others weakness e.g. can get only attacked by air units so one can't just mass zealots say in TvP against a liberator line and ignores terrain and is fast unlike a thor.
Its a complete mess. From a perfect harmony of 3 well thought out units to 4 units that is less efficient at the same task at hand into 2 additional units that make others redundant or don't have any real advantage as into why they are there in the first place.
Imo all they had to do was the following:
-Replace thors with cheaper more accessible GtA AA option. Be it a goliath or something idm because it takes far too long and far too many resources to get thors only to get tech switched or magic boxed. Not only that but they are very slow. This also means that you won't get viking vs viking wars because I can go with a ground unit to offset that air advantage**.
-Tanks need to be lower supply/cost less or simply do more damage to certain types e.g. massive/light or shields. Especially against protoss. I think this has been spoken out for the past 5 years.
-Hellions/hellbats are somewhat ok but i always liked the idea of hellions with abilities to drop flaming bettys (forgot the TL user who suggested this idea) to zone space or add more to the meat shielding because the transformation between one type to another is so cumbersome.
**I really dont like how they are putting TOO much emphasis on air units especially AtG options at each races disposal. Air units are far too powerful throughout this game without the proper ground AA units. The air vs ground dynamic is too onesided imo and there was a reason why most AtG attacks were pitiful in BW other than capital ships..