I don't think zekdonk (or ZPS as pokefreak called it) should be tier 1. I'd say tier 2 at best. the reason for this, is if you go second, then your opponent has plenty of time to get pokemon onto the bench now that supporters can be played first turn. they could even just start with 2 pokemon (causing you to need seeker from the start as well) or 3+ pokemon making donk impossible.
and if you go first, you'd somehow have to get 3 energies (or 4 if you don't start with zekrom as your active) and get shaymin, zekrom and/or pachirisu (depending on what you start with) in your hand to play onto the bench. that'd have to be a very good start hand to get what you need. and even if you do, if your opponent starts with reshiram or zekrom, then there goes your plan unless you amazingly got pluspower as well.
and the entire deck is based on early-game speed. I've tried many variations and no matter what I do, I'm always scrambling the rest of the game if the first turn or two don't work out for the donk (and it usually doesn't). I've lost every time against reshiboar and I usually lose to the other decks.