Is there a reason assassins are being picked?

I think Riot has made it clear that blowing up ranged adc/apc or anyone from melee range is a BIG no - no. Forget about it.

Yasuo is the only viable melee mid laner in the current meta and that is because his engage style is anything BUT melee. He doesn't hard commit, he has dash and windwall to ensure he avoids the insta 5 v 1 retaliation that all other melees face and a good chunk of AoE damage.

This is particularly aimed at Zed. A champion that needs to hit a wonky, slow and unreliable skillshot that honestly doesn't do that damage even if it hits on top of going full engage mode to HOPE to kill somebody (yet failing most of the time) with no CC and no actualy BURST damage other than his delayed ult. He's completely worthless in Pro play and even in solo Q unless fed off skirmishes which is a solo Q thing.

Fizz has also been a complete waste of a pick....he can have all the tools he wants but ranged dps TM and ranged Auto attack cs makes him worthless. He doesn't ahve the burst to kill anyone. Unless ahead...which again as stated, a melee champion simply does NOT have the tools to get ahead in competetive play unless very lucky.

The exception to this rule has been irelia. You have to keep in mind she happens to have like 50% CC reduction in her kit which is the reason she can actually dive and put in two auto attacks onto a target. Her kit was created to counter a super hard CC spam meta which is basically what the current meta is except there's now a Ranged ADC to benefit off all that CC.

When all is said and done, stop trying 'assassins'. They are all solo Q only stompers that don't do SHIT because guess what...everything they do a ranged champion can do better, on top of being ranged. Ahri has more dashes, damage and safety than zed, Jayce does more burst than kassadin with just his E+Q combo and Syndra can 100-0 a target sitting behind enemy lines with an instant stun much better than Fizz can in his wettest dreams. Orianna R in itself has much more chances of winning you a game than the entirety of a Zed, Fizz, Kassadin, Kha all together diving one adc. (btw kha pick only works because he has a 50% long ranged slow, his actualy kill potential is about as much as a full tank soraka).

I think once Xerath/Ori/Syndra/Yasuo are the only mid picks being taken we'll actually have a competetive worlds instead of the team with Zed/Fizz auto losing