Lass would be pretty broken, one player just unloads all of their trainers, plays it, hopes the opponent prays for a topdeck and would win. Im already not liking Ghetsis being released but at least it doesnt hit supporters.
You do remember that the cards in your hand can't have come from a Supporter, right? If you try and hoard your Trainers, you are taking the risk of being hit with a
Lass by your opponent while also making it so you can't use
N or
Professor Juniper (as those would shuffle away or discard your hand... preventing you from hording cards to unload before using
Lass on the next turn).
Lass was effective (but not a staple) back in the day because it was a format where everything was a "normal" Trainer, what we call an Item today. You play out your hand (including periodic discards for exactly what you needed via
Computer Search and
Item Finder) before refreshing it and repeating the process over again with a
Professor Oak... with the occasional
Bill added in for good measure. It was pretty easy to burn through 10 to 20 cards before using
Lass and forcing your opponent into top deck mode, at least as far as their Trainers were concerned.
This is now... your hand is probably somewhere between three and five cards and they won't all be Items. The hand is not a safe place for cards now unlike back then (
Imposter Professor Oak wasn't worth it in competitive play), yeah, you probably won't run
Lass unless:
a) Your deck has Pokémon based draw power
b) You are running a TecH copy in case you have a killer set-up and want to take a chance of protecting it.
tl;dr: Good luck trying to save up a large amount of Items to spam before using a hypothetical
Lass Supporter; one Supporter per turn coupled with disruption already present makes that difficulty. It would be a useful card, but only in the right decks or at least correct circumstances.