In the following summary I will be using these pages:
I decided to exclude ST 2 as it, despite providing a fairly interesting sample size, didn't feature matchup statistics on liquipedia. Maybe another day . Worth to mention that it was won by a Zerg player, while Protoss and Terran split the starleagues.
Let's start with GSL:
(9) Classic, Dear, herO, Hurricane, Hush,, Patience, sOs, Stats, Trap
(13) GuMiho, Maru, aLive, Bunny, ByuN, Forte, INnoVation, jjakji, Keen, Special, Ryung, TIME, TY
(10) soO, Curious, Dark, Elazer, Leenock, Losira, NoRegreT, Rogue, Scarlett, Solar
vs 16-17 (48,5%)
vs 25-24 (51%)
vs 21-23 (47,7%)
Incredibly close results in all matchups, the Terran race lagging behind in both TvP and TvZ can be easily explained with their overrepresentation in ro32 and quick elimination of the outliers going into the ro16 (Only 6 out of the 13 advanced, notable dropouts: Maru with 0-4 vs jjakji and Solar and Ryung, with 0-2 vs INnoVation and combined 3-2 vs Hurricane).
The maps behind GSL's succes?
Abyssal Reef, Ascension to Aiur, Frost, Newkirk Precinct, Odyssey, Proxima Station, Whirlwind, Acolyte, Mech Depot
Notable outliers in terms of winrate (maps where the winning race had an advantage of at least 3 games; matchups where 1 race exceeds 80% WR are underlined):
Abyssal Reef. vs 7-4 (63.6%), vs 2-6 (25%)
Newkirk Precinct vs 2-5 (28.6%), vs 1-4 (20%)
Acolyte vs 0-3 (0%)
Mech Depot vs 0-4 (0%)
Ascension to Aiur vs 7-1 (87,5%)
Odyssey vs 6-1 (85.7%)
Proxima Station vs 2-5 (28.6%)
Comment worthy is the domination of Protoss on Odyssey, the only Terran to beat Protoss there was Bunny vs Dear. Zerg obliterating Protoss on Ascension shouldn't be much of a surprise, but their record on Mech Depot and acolyte vs Terran is a sign of the hydra bane era.
(4) Classic, Dear, herO, Stats
(3) Maru, INnoVation, aLive
(3) Dark, Solar, ByuL
vs 24-29 (45,3%)
vs 18-10 (64,3%)
vs 12-11 (52,2%)
SSL is a more interesting league in terms of data analysis, because of its round robin format, allowing to collect data of ALL matchups, providing a much better sample, despite smaller sample size.
Protoss proves once again to be the leading race, with 3 of the top 4 players representing Aiur. Interestingly enough, the bottom 3 players of the league, ByuL, aLive and herO represented all 3 races. Terran seems to get the short stick overall with their abyssmal TvP record and 0 players in the playoffs.
SSL Map pool
Abyssal Reef, Odyssey, Ascension to Aiur, Frost, Newkirk Precinct, Whirlwind, Overgrowth
Abyssal Reef vs 2-5 (28,6%), v 7-1 (87,5%)
Odyssey vs 5-2 (71.4%)
Ascension to Aiur vs 5-8 (38,5%), vs 5-1 (83,3%)
Frost vs 3-0 (100%)
Newkirk Precinct vs 3-8 (27.3%)
Whirlwind vs 0-3 (0%)
Comments: the winning record of Protoss vs Zerg on Ascension comes as a surprise, and most likely the effect of the birth of mass oracle. At the same time, Newkirk and Abyssal made sure to keep the race lying low while Terrans remained virtually dead on Abyssal and Ascension, WW not helping out. Fun fact: 4 of the TvP losses on Abyssal is aLive picking the map himself and losing.
(4) sOs, Zest, Patience, Hush
(3) Byun, Bunny, jjakji
(3) Impact, Rogue, soO
vs 10-4 (71,4%)
vs 3-12 (20%)
vs 28-24 (53,8%)
No sugarcoating this: the statitics point out, that despite highest representation, all 4 Protoss players SUCKED in SSL Challenge. In fact, they netted themselves the 4 last spots. Yes, the 2016 GSL winner Zest and the 2017 GSL finalist sOs placed behind jjakji and Impact. So, why was that?
Abyssal Reef vs 8-3 (72,7%), v 0-3 (0%)
Odyssey vs 1-4 (80%%)
Ascension to Aiur vs 2-7 (22.2%)
PvT in Challenge becomes a nightmare on the maps that were favorable in Premier. Interestingly, despite the overall losing winrate, Zerg wrecks Terran on Ascension to Aiur.
OVERALL STARLEAGUE STATISTICS
vs 50-50 (50%)
vs 46-46 (50%)
vs 61-58 (51,3%)
Amazingly enough, both Protoss matchups were PERFECTLY balanced and the ZvT was only by 1,3 percent point off the perfect balance (3 maps in 119 played).
Despite Protoss massively underperforming in SSL Challenge, it seems that their records in SSL Premier and GSL were enough to elevate the race to reasonable winrates.
Since the Korean leagues use different maps to the ladder, let's look at the maps used in both starleagues.
Abyssal Reef...........19-10 (65,5%)..................5-12 (29,4%).............13-11 (54,5%)
Ascension to Aiur....7-11 (38,9%)...................14-10 (58.3%)............9-9 (50%)
Odyssey...................8-5 (61,5%)....................12-5 (70,6%)..............9-8 (52,9%)
Newkirk Precinct*.....6-9 (40%)........................6-13 (31,6%).............4-4 (50%)
Frost*........................6-6 (50%)....................... 4-1 (80%)..................2-1 (66,7%)
Newkirk Precinct and Frost, as marked with the bolded asterix, are the only 2 of these maps that weren't featured on the ladder at the time.
Bolded are the matchups where one of the races reached 60% WR or above, Out of these, only PvT on Frost with a sample of only 3 games seems largely irrelevant to any balance statements on the map itself.
Zerg's overwhelming power (and especially power of hydra bane) is well known on Oddyssey and Ascension to Aiur
Interesting seems to be ZvP on Newkirk Precinct, where Zerg holds horrible 6-13 record and, despite that, Zerg players chose to play the map instead of vetoing it. Similar case occurs in TvZ on the map.
Another interesting thing is the TvZ winrate on Abyssal, where Koreans Zergs seemed to struggly greatly. With with hydra bane, it's interesting how the map will play out at Blizzcon.
ZvP on Abyssal also seemed to be a torture, partially because of the mass oracle playstyle that developed in later months of the leagues.