I think comparing single units from different factions, which do similar things, is not the right way to approach balance.
I would disagree, as both units share the same purpose; To cover your army/navy.
It's better to have one factions mobile shield to be (considerably) worse than those of other factions, if it has other means to compensate. Otherwise every factions would just have the same units.
And just having slightly different stats, but having each unit balanced to it's counterparts, is boring balance.
You are correct. If all units or similar units are basically the same, then it won't be diverse and fun.
Though, this is why I offered 2 suggestions. For this situation we choose option 1: lowering the maintenance cost, we still keep the unit stats the same, though the Energy maintenance is a tad lower.
if it has other means to compensate
I understand your point here, however, I'm not sure if the UEF can compensate for an inefficient shield - at least not in an obvious manner that I can see. Would you care to share some more insight on this?
So an unit that is used and does it's job for the faction (and the faction is not just worse than the others) should not be buffed.
And if a faction is worse than others, buffing their strengths instead of fixing weaknesses would be a more fun way to go.
I believe this is where the second option could shine. With these changes, the Parashield would have a larger shield radius, covering a larger army, whilst the Aeon Asylum can still have its multiple uses (considering hover), and basically cover its units in a tighter area more effectively. One large expensive shield vs one small tight shield, if that makes sense.
Yes, they would have the same HP, but the Terran mobile shield would have a slightly more versatile use in the land game.
In other words, one multi-use shield (land and sea) vs one dedicated shield.
The changes in its costs would also reflect this - being more expensive than the Asylum.
Thanks for your feedback!