What Leicester did will be better than Leverkusen, Leicester were almost relegated, somehow they went on a mini run to save their PL status and next season they got 81 points which itself is an incredible achievement.
Promotion from championship, saved from relegation in last few games and then PL title. That's amazing.
Leverkusen were always around top half, CL-Europa place team.
Yes IIRC Leicester were joint 16th favourites to win the title at the start of 2015/2016 season, alongside Sunderland, and behind Swansea, Crystal Palace, West Brom etc. Only the 3 promoted teams, Norwich, Bournemouth and Watford ranked below them there. They also started the season with either the 4th or 5th lowest wage bill in the Premier League I think.
At the start of the season, I doubt anyone thought that they'd finish in the top 10 (which they hadn't last done since the 1999/2000 season for perspective) or above Mark Hughes' Stoke team for example that had finished 9th during the 2 previous seasons. I doubt many people even thought that they'd finish above Tony Pulis' safe and steady West Brom team.
Leverkusen finished no lower than 6th in the league and qualified for the Europa League (at least) during each of the 6 previous seasons, and during 13 of the 14 previous seasons. IIRC they were the 4th favourites to win the title at the start of this season, behind Bayern, Dortmund and Leipzig.
There's no serious comparison at all there.
Of course Leverkusen have been absolutely brilliant this season, a lot of fun watch (including yesterday when they were by far the better team and could have won by an even bigger margin), and I really hope they go on to win the title, which if they do would still be a outstanding achievement.