Our cycle has an advantage of not being roflstomped right when the Reapers arrive and having access to mass relays.
The relays have nothing to do with most of the reapers lost in this cycle, only the construction of the cruicible itself. The massive Reaper losses, several capital ships, at Palaven were destroyed by the Palaven home fleet when they launched a suprise attack on the system. Likewise the losses of process ships, transports, destoryers, and capitial ships they lose on the surface were by suicide bombers with weapons that could have eaisley been stockpiled on the surface of a militant minded species. The destroyer on Earth is not killed with ship born weapons even, just a ground side missile, yes the reapers could screw with the guidence system but it wouldn't be that hard to simple remove that system and fire a barage ala rocket attack style. Yes, the relays are ctitical to resistince on a galactic scale but not the reason why local forces were able to inflict individual losses on them.
That's because the protheans couldn't even use their superior military strenght against the Reapers because they had no intact relay system to gather their fleets and army with. Being hyper-militarized isn't worth sh*t when each star system is on it's own without having any means to get reinforecements, more supplies and with severly limited communication between systems as well. Is this really that hard a concept to wrap your head around?
Also killing Reapers left and right? You are clearly exaggerating. The Reapers kick everyones combined ass every time they are on screen and have minimal casualties. And this is against people that were somewhat prepared for them and still had the ability to gather fleets/troops and communicate with each other across the whole galaxy. None of the previous cycles had any of those advantages.
It's not every star system on their own though, its every star cluster at least. Rember that the relays are not the only way to get around or communicate in the mass effect galaxy. Their are ftl engines capable of traveling 15-20 light years a day, a galaxy 100,000 lys wide would only take 13-18 years to travel across as long as you can find fuel, helium 3 which can be skimmed from gas giants, a planet with a magntic core to discharge the drive, and the food to survive the journey which would likly be the hardest thing to issure but could be possible. In addition the relays are only used for cross galatic communication while simple becons are used to communicate within clusters.
This is all relavent because Earth and humanity are very young and have only 1 industiral world in Earth and a few dozen colonies and mining outpost and were still capable of building a massive fleet between 2149 and 2186 including 9 dreadnaughts. Their is no reason to assume that a cluster that was colonized for hundreds of years if not thousands would be limited to only 1 industrial world and would be unable to mass produce their own massive fleet in the centruires they are left alone while the reapers are harvesting other worlds. This is reinfoced by the fact that Javick was born very late into the war, basicly the end of it, and he described fighting in diferent systems which means that after hundreds of years of war the Protheans still had ftl ships and were capable of interplantary war while eden prime is seen to be a very large Prothean world left untoched during the war until the end.
Now, all these facts are irrelvent because word of god overules game facts and logic which is why we have such confusion on the matter becuase not everyone, like me, can be bothered to read a devs twitter feed so we don't all get the contradictory infomation that overrules the game itself. But hey, if the devs want to say that the reapers are the stupidest evil empire of all time despite being gigantic computers who am I to argue.