I don't think that T4 upgrade help them much. It's almost like run to uphill, where from the start to lategame you must survive until build T4 and get this upgrade. While in the other side you have penals from box, they are work from start to end and have good scale in lategame.
If we want make cons really support unit and keep penals as more expensive offensive unit, we can change cons from terms of resource effectivness, not their battle states. As i suggusted before in previous topics about cons:
1. From 1-st buildnig (T1 or T2) you get global upgrade to speed up reinforce for cons.
2. From medics upgrade you get upgrade on cheaper reinforce for cons (16 mp instead of default 20).
3. Replace flare mine to faster sandbag building.
Their decreased cost and time of reinforce will make ability Merge more attractive to use than now . Fasten sandbag will show them as defensive support unit and help play through T2.
These changes don't make them good fighters, but get to SU player 2 options: openning from cheap and fast to return on battlefield cons (without any real additional investments), or more expensive offensive oppening through penals.
Merge was never attractive, and it won't even above change. Main reason is after merged, the model/entity retain the model size > 1 (increase chance to be hit). Nobody want to lose their squad because the last retreating model is conscript and die due to some passed by volk.
Merge with shock troop means losing model quickly before shock can get to close range.
Merge with guards? Easier to drop weapon on the ground.
Merge with weapon team? Maxim death loop to remind. Mortar get cut by flanking squad without chance to react, AT Gun become easier target for tank's hull/top gun.