dude 2015 teams will beat 2013 teams. 2017 teams will beat 2015 teams. 2018 team will beat 2016 teams. and 2020 teams will beat current top teams. it will always be like that.its because of changes in skill and form of players,csgo meta and tactic changes,weapon changes,mappool changes and so on. it will change always.
there is no point comparing top teams from 2015 to 2018. compare top teams from 2015 to other top teams in 2015. similarly in compare top teams in 2018 to 2018.here we have only 2 good teams.astralis and navi.liquid is overrated,they didn't even won a single big event yet. all others are having bad form and roster issues. only teams who had stable roster is still in top like astralis,liquid and navi. all teams like fnatic,faze,sk,mouz,north etc are having issues and we are having weak top scene.
that was not in th case in 2015. there were multiple strong teams.teams like tsm,vp,nip,navi,c9 were all gunning to win events.but there was fnatic and nv to stop them
today don't have similar top level teams.only one is liquid and astralis is always stopping them.but in 2015,these teams also won big events like fnatic but fnatic were slightly better than rest. thts why fnatic have an era.
also can't you count the number of top events in 2018?