It's more of the luck of the draw/trying not to put out put the same champs in the line up too often.
There's a couple rules they follow when picking Free Weeks.
- Must have two Marksmen. The role is so pivotal in the meta worldwide that denying a new player access to them is hobbling at champ select.
Reverse order going over the past several weeks goes: Ashe/Caitlyn. KogMaw/Twitch. Graves/MF(+). Quinn/Varus. Jinx/Lucian. Urgot/Vayne. Draven/Varus. Caitlyn/Ezreal. Corki/Sivir. Ashe/KogMaw. Jinx/Quinn. Graves/Lucian.
+Kayle and TF get honorable mentions for their ADC off-meta builds.
- Must have at least two Supports. You can probably count on one hand the number of times over the past couple years where there wasn't two Support champions in the line-up (whether by kit design or what the meta deems supporty).
Reverse order: Karma/Sona (honorable mention Nidalee). Nunu/Taric (HM Jarvan, Shen, VelKoz). Leona/Soraka (HM Kayle. I know Liss is sometimes played support, but I've seen it successful less times than I've seen Support Eve win a game). Janna/Thresh (Annie). Blitzcrank/Zyra (Volibear). Lulu/Nami (Brand). Karma/Morgana. Zilean(+). Braum/Lux (Malphite, Maokai). Leona/Thresh (Azir). Soraka/Taric. Janna/Sona.
+One of those weeks with no other meta Support, but the Veigar in that week does get played Support on occasion.
- Must have two junglers. Whether Riot admits it or not, they do design and balance to the 1-1-1-2 Meta. Playing with no Jungler leaves a team at a significant disadvantage if the other team is using one.
Reverse order: Aatrox/KhaZix/Rengar. Jarvan/Nocturne/Nunu. Diana/Hecarim/Olaf. Yi/Shyvana (GP). Amumu/Volibear (Sion). Rammus/Sejuani/Tryndamere. LeeSin/Vi. Pantheon/Xin Zhao/Trundle (Gragas). Maokai/Udyr. Skarner/Wukong (Nasus). KhaZix/Rengar (Fiora). Aatrox/Udyr/Zac.
They also like pairing up rival champions. You see Leona and Diana a lot in the same week, and I don't recall a time when Rengar was free and KhaZix wasn't.
After all that, it's rare that you have to stretch too hard to make two viable teams out of the 10 given. I'll give two examples.
Seven weeks ago, the one with only Zilean as Support.
- Team A: Ezreal, Pantheon, Kassadin, Renekton, Xin Zhao.
- Ezreal and Pantheon Bot Lane. Not the best spot for our beloved spartan, but his target stun and initiation shouldn't be ignored. He has targeted harass with the spear throw, and with the rest of the team having a pretty high AD focus, Zeke's Herald is a great buy for him.
- Kassadin Mid, Renekton Top, Xin Jungle. This team has a heavy focus on mobility and bringing the fight right to the enemy. Their collapse should be good at all points of the game, and the only threats are the late game Trundle and fed Caitlyn/Veigar. Their fallback pattern is a split push with collapses in the jungle.
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- Team B: Caitlyn, Zilean, Gragas, Trundle, Veigar.
- Cait and Zil Bot is pretty damn safe and would likely need the enemy jungler's intervention to disrupt it. Veigar is a little (ha!) exposed in Mid, and it will likely be their weakest role. Gragas Jungle ganks are not to be scoffed, and putting Trundle top gives him the farm he needs to split push and duel all day against most of the enemy team.
- Focus is on the Team Fighting, using Gragas to engage from the side with a well timed (ha again!) Zilean bomb, followed up with Veigar stun as the carries unload on who ever gets caught out. Zilean's Ult can bait out a fight or save a bad play, and Trundle's stat stealing can ruin the enemy's AD focused and low tanking team.
- Fallback pattern is a defensive strategy to mitigate the oppressive split push the other team has in spades. If the opportunity arises, they HAVE to go for the team fight and most likely will try to contest every Dragon and Baron.
Against each other Team A has the higher chance of success. Their champs are more self-reliant and naturally safer due to mobility. It mostly comes down to skill, though an even match will favor A if there's not early game throwing in B's favor.
Eight weeks ago.
- Team A: Braum, Malphite, Maokai, Orianna, Sivir.
- Focus is on the obscene AoE damage Ori and Sivir can deal while Braum, Malph, and Maokai keep the other team locked down. This is Team Hard Engage right here, though each champion does have access to some level of poke for a fallback pattern. Malphite Top and Maokai Jungle.
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- Team B: Corki, Lux, Udyr, Vlad, Zed
- Focus is on their great disengage with split push potential. Come mid/Late Game, Corki and Lux stay mid while Zed, Vlad, and Udyr roam and split the other lanes. Take note that while their CC is low, their single target focus and mixed damage along with safe poke means it's unlikely their tower defending will be easily crushed.
Facing each other, it's likely that if B can't gain a significant advantage early, they'll have to bring a really good poke game to handle Ori and her wave clear and two ball delivery allies.
Considering I've already been at this post for over two hours, I'll leave out trying to make two teams with the current FW Champs. They're there though, and honestly, it looks like a brutal brawl with so little naturally tanky options.