In 2015, the League of Legends Mid-Season Invitational tournament was created. In response to the lack of international events and schedule tweaks across all regions, Riot Games created a longer mid-season break between the spring and summer splits to accommodate a new tournament.
At the time, South Korea had undergone significant structural changes. OnGameNet's Champions tournament become LoL Champions Korea, a new eight-team league -- expanded to 10 teams that summer -- and sister teams were abolished. Instead, 10-man lineups were permitted, and to some extent encouraged. Organizations could not have two separate teams of five, but they could have a team of up to 10 players.
Yet this was not supported or encouraged at international events. The 2015 MSI rule set stated that only five players were to participate in the starting lineup with one player available for substitution. This has not changed, although teams are allowed a seventh player in case of injury or illness. For all intents and purposes, the seventh player was not part of the lineup.
In 2015, SK Telecom T1 had to choose which substitute the team would bring to MSI. Most players, coaches and analysts used coach Kim "kkOma" Jeong-gyun's swapping between mid laner Lee "Easyhoon" Ji-hoon and Lee "Faker" Sang-hyeok as the definitive example of how to use a roster substitution due to SKT's visibility at the inaugural event. However, the team had also experimented with two junglers (Bae "Bengi" Seong-woong and Im "T0M" Jae-hyeon) and two supports (Lee "Wolf" Jae-wan and Lee "Piccaboo" Jeong-beom) during the 2015 LCK regular season. Easyhoon was SKT's chosen sixth-man during a volatile split where SKT was transitioning from two sister teams of five to potentially larger lineups.
When considering why the rule for only one substitute is in place, the thought that those organizations with only five or six players would be slighted should another team bring 10 often comes up as a response. Yet, this is a specious argument. The ROX Tigers are an example of a team that made it to the World Championship finals twice, first with the roster of five founding members in 2015 and then with another roster of five in 2016 (substitute mid laner Hae "Cry" Sung-min was not listed).
In 2017, no sooner had SK Telecom T1 lost 3-1 to Longzhu Gaming in the League Champions Korea final did the discussion of how SKT should fix its problems began. It even drowned out accolades for Longzhu and its top laner Kim "Khan" Dong-ha. SKT had been the default League of Legends representative of South Korea at international events, and while it qualified for the 2017 World Championship, Longzhu had exploited SKT's largest weaknesses. Now, SKT had to address the team's issues quickly, all while choosing one substitute for the upcoming World Championship.
Between its two junglers, Kang "Blank" Sun-gu and Han "Peanut" Wang-ho, the team also had to make a choice between two top laners, Heo "Huni" Seung-hoon and Park "Untara" Ui-jin. Although SKT truly relied on a seven-man lineup, the rules allowed the team only one substitute. SKT chose a more aggressive top laner Huni -- presumably to prepare to face Khan -- over Untara and brought both junglers instead. It was a sensible choice. Huni created more pressure on the top side of the map and could hold his own against Khan, unlike Untara, yet it still stifled a certain facet of SKT's play. The team had made it to the 2017 summer finals using a seven-man lineup, but was not allowed to bring that full lineup to the World Championship.
A similar scene played out recently after Royal Never Give Up won the 2018 LoL Pro League spring split, qualifying as China's representative at the 2018 Mid-Season Invitational. RNG relied on a rotating seven-man roster for the majority of the split that included two junglers, Hung "Karsa" Hau-Hsuan and Liu "Mlxg" Shi-Yu, and two top laners, Liu "Zz1tai" Zhi-Hao and Yan "Letme" Jun-Ze. Unlike 2017's iteration of SKT, where there was arguably a more clear-cut decision on who to take, RNG created diverse strategies and strengths around both junglers and both top laners.
Karsa is a more stable, standard jungler who gives up fewer map advantages on the map than Mlxg, yet Mlxg's lane-focused playstyle has previously taken opponents by surprise on the international stage, with his synergy alongside mid laner Li "Xiaohu" Yuan-Hao stronger. Zz1tai focuses on in-lane trading and draws more pressure to the top side of the map, but LetMe understands minion wave pushes a bit better and has stronger zone control in teamfights. Both allow RNG to set up the team's preferred 1-3-1 split push in the mid-to-late game, but the style of execution varies, which can keep opponents guessing. RNG chose to bring both junglers with LetMe as the team's starting top laner, yet the loss of Zz1tai's top lane pressure will be missed. The MSI substitution rule actively hampers RNG's flexibility as a team, which earned them the title of LPL champions.
Having more players on a rotating lineup does not guarantee that a team is better. In fact, rotating through substitutes in a cohesive way that doesn't jeopardize a team's synergy is more difficult than simply focusing on a starting lineup of five. Samsung Galaxy made it to two World Championship finals and won the 2017 iteration with a six-man roster. In both cases, Samsung barely played its sixth-man. Support Kwon "Wraith" Ji-min played two games in 2016 over Jo "CoreJJ" Yong-in, and jungler Kang "Haru" Min-seung played one over Kang "Ambition" Chan-yong. With nothing proving that larger lineups have any sort of competitive advantage over a unit of five or six -- again, it's arguably the opposite, a strong core of five starters synergize more quickly than a larger, rotating roster -- it's time to stop punishing teams like RNG that do manage to have a variety of strategies around more than five or six starters.