I don't think it's fair to judge whether Black Clover's a success or not based on how Toriko did. Toriko was airing next to One Piece and had a far greater exposure than Black Clover. WT is a much more apt comparison and correct me if I'm wrong but its sales didn't increase much until the anime was halfway through.
World Trigger had actually grown quite a bit by the time it reached the halfway point of its anime. The entire run went from Fall 2014 to Winter 2016. That puts the halfway point around the end of Spring 2015 to mid Summer 2015. This is the transition from beginning to the halfway point to the end of Summer 2015:
│*69982 (3)│114309│------│------│------┃*,114,309 (*10)┃2014/10|ワールドトリガー 8
│153824 (7)│185799│******│211593│------┃*,361,399 (322)┃2015/01|ワールドトリガー 9
│156001 (5)│206563│229063│******│257245┃*,371,416 (264)┃2015/03|ワールドトリガー 10
│167149 (4)│227858│254340│269102│------┃*,350,637 (172)┃2015/06|ワールドトリガー 11
│147368 (3)│241891│272018│292349│------┃*,325,690 (*80)┃2015/09|ワールドトリガー 12
You can see by the end of Summer 2015 it had grown quite a bit from the beginning back in Fall 2014. This is the remaining of its anime run:
│146833 (3)│243294│273241│292706│------┃*,392,138 (353)┃2015/12|ワールドトリガー 13
│156433 (3)│257631│289571│******│319631┃*,381,789 (262)┃2016/03|ワールドトリガー 14
and this is post anime:
│159437 (3)│264097│295120│313678│------┃*,375,944 (171)┃2016/06|ワールドトリガー 15
│143333 (3)│250253│282655│304311│------┃*,344,137 (*80)┃2016/09|ワールドトリガー 16
│133843 (3)│243575│277049│******│310657┃*,357,667 (171)┃2016/12|ワールドトリガー 17
│137262 (3)│241796│275748│------│------┃*,332,766 (*80)┃2017/03|ワールドトリガー 18
Keep in mind that towards vol 17, it had already entered hiatus but it didn't grow too much after the halfway point. This is true for most series. The biggest boost tends to be at the beginning and it slowly tapers from there. Few series are able to keep the height of the initial boost throughout the entire run, especially for a run longer than 1 cour. I've only seen AOT keep the full momentum throughout its entire run.