err Nome, you dont need to be farmed with those heroes, that is precisely the main issue.
This is not LoL, skills don't scale with items (except for RA's W, but he has a base nuke damage as well). Most S2 heroes have great early/mid/late games, which is the reason why they are usually OP. Both of them have strong nukes and insane farming ability (better than 90% of heroes in game easily). Once Zephyr hits lvl 6, he drops ult on you, and gust, hero pretty much dies unless you have a blink. Once RA hit lvl 5, his Q and W pretty much instantly kills any INT/AGI heroes. This makes snow balling much easier for those heroes. If they gets shut down early game, they can easily clear out jungle to get back into the game.
All heroes should have some sort of weaknesses in order to be balanced, aside from RA/Zephyr/Silhouette, other S2 heroes are okay, but still out perform most original DOTA heroes.
Lets take Drunken Master for example. When the hero first came out, he is extremely strong and viable for mid. He can control the lane very well. However, he couldn't farm for shit (and that was his weakness). Once S2 addressed that weakness, you see more of him in TMM matches, and even in league games. Geomancer falls into that group too, it is a decent hero, but cant farm and doesn't scale well.
The line up you mentioned is still very viable in DoTA, and actually proves my point. In a team based game it make sense to pick a team that can initate / turtle / gank / teamfight effectively. I don't think anyone wouldn't replace those heroes with heroes like huskar/troll warriors/ursa etc. Same reason why I wouldn't pick any other carries other than RA/Silhouette/Zephyr.
Allow me to make a comparsion in LoL. How many time have we lost in Dominion after a 300 points lead, and lost to 1 champion because he/she is extremely OP? This happens in regular league as well; there are just champions that out lanes majority of champions. It makes no sense not to pick them over others.
Its like DOTA2 right now as well, it doesnt make sense not to pick either Void/AM/Weaver/Spec as part of your team. I mean, how can you even argue that those heroes are not OP? lol. The difference between HoN and Dota2 is that AM/Weaver/Spec needs to farm to be effective, whereas Zephyr / RA is like giving a hero instant Bfury to help them farm and snowball.