Well I haven't lost to the Romans either in vanilla civ. But a lot of players thrive of the Praetorian UU and own a lot of AI civs at the start of the game when using them. I usually go for the culture victory (France or China) and don't use their UU's much.
But anyway, it's always risky to tweak the game balance.
There's nothing wrong with tweaking gameplay... you're assuming that Firaxis (a company created by oh-so-fallible humans) got everything in playbalance 100% correct from the get-go. Which just proves how wrong Firaxis can be, since they constantly change gameplay balance with every single patch they put out... so obviously they haven't been getting it right themselves.
I'm not of the mindset that what a game company does is always correct out of the box, nor do I treat changing things they did as taboo. All humans are fallible and that includes Firaxis.
You seem to act as-if allowing roman swords to be made of bronze (as they were in the Roman Republic) is some sort of sacrilegious change that has just completely ruined the game... I say "phooey" to that... if the Romans used Bronze Swords in history, why can't they in-game?
Personally, if you want to talk about civs being unbalanced, I'll point to the damn Malinese... I'd rather be surrounded by Romans with Bronze Swords then having a single Malinese Civ in my game... that damn Leader makes his civ 10x more competitive then all the Romes in the world.
A single UU is not going to make or break a game, and quite frankly unless every single civ has the exact same leaderhead AI and the exact same UU, the game is already unbalanced. You're thinking with a closed-mind Chuggi... it is completely impossible for the game to be 100% evenly balanced unless every civ has the same units, same leader-AI-routines, same UUs and exact same equally-distributed starting spots and access to resources as every other civ.
Crying over bronze swords doesn't mean Firaxis was astoundingly insightful as to how they handed-out things in the game... every patch changes gameplay, so every time Firaxis touches the game they change play-balance (and quite frankly, I think they ruin things the more they mess with them... the latest patch made airpower almost pointless with almost every unit under the sun having AA intercept abilities)... obviously they know no-more then you or I when it comes to play-balance (and I'd say they often know less)... they are humans after all.
I'm not even sure I want every civ to be equal in power... they certainly aren't out of the box as-is (once again, the Mali & Ethiopians come to mind). There's no way to make every civ equal in power because no two civs are equal in every regard to begin with... a Roman civ in Vanilla Civ4 that starts right next to an iron source underneath Rome is no different then a Roman civ in the Wolfshanze Mod that starts next to copper... explain to me why in Vanilla Civ4 the Roman Civ that starts on top of Iron is less unbalanced then the Roman Civ that starts next to Copper in my mod?
Bottom line, I don't feel that Firaxis is stationed on top of Mt.Olympus and should be worshiped as infallible gods.