Most serious hockey fans are familiar with the WHL, as it is part of the CHL, one of the top developmental leagues for the NHL. However, more casual fans may not understand how this agreement affects Holinka's career. For starters, he is coming from Czechia. While the country is known for producing top quality NHLers, their own leagues lag behind those in other countries. As such, Holinka will be facing tougher competition from WHL opponents than he was playing in the Czech junior league. Second, he will get a chance to adapt to the smaller North American ice surface well before making the jump to the NHL, which could be very beneficial to his development. These are among the things Miroslav was probably considering before agreeing to the deal.
With that being said, the stakes for Holinka at the current moment are rather low. The Leafs drafted him in the 5th round, 151st overall this year. Generally speaking, the vast majority of players drafted in his position never make it to the NHL, so he might as well choose whichever development path he thinks will give him the best odds of making it. Coming to North America early certainly doesn't hurt.
Holinka has 20 goals and 41 points in 29 games at the U20 level in Czechia last season and an additional 1 goal and 3 points in 16 games at the pro level. He also represented Czechia at both the U19 and U20 levels where he recorded 8 points in 4 games and two points in three games, respectively. Did the Leafs find a diamond in the rough in Holinka? Keep an eye on him over the next couple of years to find out.