UngeheuerLich
Legend
Mate, you can build an entire party with 20s.
Cleric with a 20: battle or laser, either is fine.
Fighter with a 20: use a board, and you can tank. Marks are a credible threat rather than just a "hit me" sign.
Striker with a 20: archer or rogue, take your pick.
Wizard with a 20: self explanatory.
Go ahead and try to swarm.
That party will wipe out swarms with ease .. now, I counter your challenge.
Build any encounter, throw it against that party, and see how much more dangerous it is against your balanced party.
yes, that whole party sounds quite good with only 20s... if you pick battle cleric and rogue, i will pick ranged and flying...
if you pick striker or laser cleric, i need a bit more time and i need to see the full writeup...
maybe something that can teleport up to your wizard, the ranger or the laser cleric which, if not prepared for melee will go down pretty fast... maybe the cleric is the weakest part...
mix in something that can attack your fighters will defense and it could get funny...
also i would use brutes, not soldiers, because soldiers best weapon is their AC and Attack bonus, which is not so important if your chances to hit are too big...
maybe the best would be following challenge: you build a party of 4, i build a party of 4 with each role covered once (maybe a second striker may replace the controler) at level 1, 5, 9 and lets see how they will compare... (note: i will not hesitate to also put a 20 into an attribute if it is the logical thing to do...) i may use the full standard array/point buy.
You are restricted to using those with 18 in the prime stat for all characters... you may or may not take a race, that increases that 18 to a 20...