I never, ever suggested giving up. Don't put words in my mouth. The best strategy for a city defense army is a mix of current and higher (if you have them) units. What I said was that it would take a huge edge in relative boosts to have any chance of stopping a 1+7 attack, and that setting (and changing occasionally) the mix defense is to be accompanied by a practice of collecting on time. I stated this before if you would bother to read instead of making up what you think I said.
Well, if you're not a good fighter, then what units give you trouble is rather irrelevant, The best way to beat your 3 Heavy/5 Artillery mix varies depending on the era. From Iron through Colonial, 1 Artillery+7 Rogues will defeat it rather handily. Usually without taking so much as a hit, let alone a lost unit. In Industrial, I would use 1 Rifleman+7 Rogues. Might take a few hits, maybe even lose a unit, but still not a problem to win. If you have a Traz (and if you're a serious player, you would have one by then), then losing a Rogue or three is no big deal. In PE I would go back to the 1 Artillery+7 Rogues, as the PE Tanks are slow as molasses and easily picked off. Probably use the same in ME, although that is the age I have the least experience in (or at least the haziest memory of the battles.) PME is good for the 1 Artillery+7 Rogues again. In CE, the AAV with 7 Rogues will wipe up the battlefield with 3 Heavy+5 Artillery, although there will be some small damage taken due to the special ability of the CE Missile Artillery. That's all I have time for now. Maybe I'll edumacate you on the higher ages later.