Well, thats not the only thing modded... as I said, some civs can handle it (as long as you don't put Raging Barbarians on) without losing their cities.
I have one modded civ that has Montezuma's personality, who has a UB version of every building or unit that has a UB, and has all leader traits, not just two, and I also have a playable "Minor" civilization with no UB, no UU, and no traits.
The personality of Monty, with gunpoweder units starting at combat 1, drill 1, CG1, all units taking 3/4 experience to promote, and all the other benefits of the other leader traits.... combined with other civs that are generally weak due to barbarian incursions... on a continents map, Generally results in an unstopable war monger who ends up owning the whole continent.
If he's on the same continent as you... yea, it can be challenging, especially if you play as the Minor civ.
Or play at a higher play difficulty level, where the modifiers are the same, except for the bonus vs barbs
If one plays on a terra map, where the old world is rather packed, the barbs are a short lived problem, and if the Super-Monty civ is there (either randomly, or specifically placed there), it can be very tough.
I like to see some civs struggle against the barbs, I generally add a few extras as well, anticipating some will be wiped out.
I prefer to see in my games some other civs that struggle and collapse, and others that are juggernauts.
And of course, if you know you will win, the question is, how fast can you do so?
Removing the AI bonuse vs barbarians was an experiment to see what would happen, and it was clear they can't handle the Barbarians without bonuses, as is.
So I further tweaked, and further tweaked, to get a dynamic I like.
The current iteration involves all capital cities being naturally well fortified, a map slightly crowded with civs, and at least 1 super civ (currently considering an other super civ just like the other one, but with a more cultural/technological focus- ie Mansu Musa or Ghandi's personality, and a different selection of UU and UB when there is more than possible one UU or UB replacement candidate).
An expansionist, but normally not warlike leader, would benefit from other civs stuggling to deal with barbarians, if it could easily deal with barbarians, given that it has CG1, drill Bowmen, and the bonuses to construction speed of Duns, giving bowmen guerilla 1.
Normal civ games often have similarly sized civs, civs are rarely destroyed from anything other than the players actions, while some civs become significantly more powerful than others, they rarely completely dominate.
All that changes in the versions I play.
My current game, I own about 1/3 to 1/2 of my continent, killed the "minor" civ before anyone considered it a friend and took its land, liberated cities from the barbs for two of the other civs and got us all on the same religion, they both volentarily became my vassal, leaving only 1 non vassal civ on my continent, who is currently pleased with me, things are looking OK for me, except its a domination/conquest victory condition, and as I am still tweaking, I use WB to check up on how super Monty is doing...
He's already defeated two other civilizations (both which had lost cities to the barbarians), and has about half his continent, I suspect by the time astronomy rolls around, he'll have the whole thing.
OOOH, I used WB.....
OOOOH I don't use the standard version
OOOOH I use edited maps.
Who cares, I'm not dishonorable or dishonest, I'm playing a game and not harming anyone.