Upkeep is IMO a very flawed idea at it's core and i've never liked it in any game i've played. It's supposed to give the struggling player a bit of a helping hand by giving them more money than the other player, but it wrongly assumes that being behind means having a small or no army at all. One would think that preserving ones army when behind is of utmost importance, but in Dawn of war 3 you'll actually be punished for it, as the game sees that you have a nice army and therefore thinks that you shouldn't have any more resources.
I've noticed that this leads to somewhat of a "throw-away" meta, at least in 3v3s which is what i mostly play with my friends. I've lost so many games to teams that just throw an endless amount of expensive units at your base, with little to no effort of actually being even remotely effective with them. This is of course because when they control the larger part of the map and throw away all their units, that by the time that i'll have reinforced and marched my slow wraith-based army (because you're just not going to win games with fire prisms, honestly), they will easily have mustered up a new, at least, decent army.
The problem is just that there's really no scenario where upkeep is actually going to favour the player that's lagging behind. People say that without upkeep, you could just quit the game after loosing the first skirmish, but that's clearly not true since upkeep doesn't kick in until 30 supply. "But what if you're behind AND you lose your army?" Well then you're dead anyways, no wonky economy modifier is going to save you, sorry.
To me there are three major scenarios where upkeep really matters:
1: In the early game where i try to stay under 30 supply to max my power income
2: When you're minutes away from winning a game, your army gets nuked by something silly like orbital bombardment or a weirdboy-roks-combo (please remove it) and you go "HOLY ++heresy redacted++ I HAVE A LOT OF MONEY"
3: When you're making your last stand at the core and you're literally killing endless waves of space marines and dreadnoughts and barely losing a single unit but you're still never going to come back because the opposing player is just getting so rich from playing badly.
Notice that none of these mention anything about coming back from a tough game thanks to a little help from the lovely game mechanic that is upkeep. If you disagree then i would love to hear why, because for me upkeep seems like such a bone-head mechanic that does nothing good for the game and needs to go faster than you can say "why do dire avengers overheat?". Perhaps the game would be more one-sided than i imagine if upkeep was completely removed, but i do know that in it's current implementation, upkeep is just not a good mechanic.
tl;dr: I wish the game would punish you, not reward you, for playing poorly, and i'd love to at least try what the game would be like without upkeep.
EDIT: I should add that this post is mainly about the later stages of the game, where, as mentioned, if you're behind and you lose a big fight you're dead anyways, and if you're behind and actually managing to preserve your army then you won't get any resources and thus inevitably, most likely, lose the game as well.