I played the mission on hard and I liked it quite a bit but there are some things that could be worked on. I didn't get to complete mission as of yet but I'll give it another try soon. The first stage of the mission seems quite well balanced and getting the objective done in the time given (20mins?) can be done with good strategy and play.
Now the second stage seems a bit unbalanced. The moment you complete the objective so the map expands or if you just wait for it to expand you get multiple t2 transports dropping t2 and t3 units in and around your base. Now you can't really kill a significant amount of these t2 transports without insane amounts of t1 aa and mobile flak before they drop which is fine but there are 2 scenarios that are likely to happen at this point. 1. You completed the objective in the given time and most of your units and your acu are in the enemy base so your base gets destroyed by the rhinos and loyalists. 2. You didn't complete the objective in the given time and you have most/all of your units in or close to your base including your acu so you can defend the drops and continue the mission without your base taking too much damage. The scenario 1. is way worse than 2. so there is no real reason to complete the objective since your base will take significant damage or get outright destroyed.
I propose 2 solutions. 1. Succesfully completing the objective would reduce the amount of drops and they wouldn't be in your base but around so you could defend the more vulnerable infrastructure more easily. 2. Give a bit more time to complete the objective so the player can build more units to defend and perhaps retreat the majority of their units that were attacking.
Now the rest of the 2nd phase. The opponent having access to t3 land and t2 air isn't really fair. Pillars lose to rhinos in equal numbers and loyalists are even worse and since the opponent isn't short on mass we don't need to compare mass to mass. Perhaps enabling the titan to be built would help a bit. T2 air isn't as big of a deal since inties and flak do a fine job at keeping them at bay. I wouldn't mind the ability to make some gunships or fighter/bombers.
The mission is focused on assault so I understand why you have disabled defensive t2 structures but at least having the shield would help a great deal against t2 air and a bit against the land forces it would basically just be a better variant of the mobile shield. Stationary flak could also be available since the mobile version is available. The ACUs personal shield upgrade could be made available to help in the 2nd stage but it could make the ACU too good, hard to say.
Edit: Replays only seem to show the first stage of the mission.