It wouldn't be in this crystal based on how they described the event
is it just me or greater crystals (lower tier) has better items in them?
Just you
It depends a lot on the actual drop rates, which we don't see. I'm also not sure if the lower-ranked crystals are part of the Jubilee grace system. It's possible that all possible rewards are in the lower-ranked crystals (but at very low drop rates), while the top rewards are cordoned off from the general drop rates of the top crystals and then given out on a guaranteed basis via the Jubilee grace system.
Let's say that there's a 0,5% chance to pull a Titan Nexus (or something of equivalent value) in the lower-rank crystals. It tends to be some kind of super low number like that. Now compare that to a 100% chance to pull a Titan Nexus (or something of equivalent value) from a Jubilee crystal for every 15 higher-rank crystals you open. That's a huge difference in the higher-rank crystal's favor, despite there seemingly being "better rewards" in the lower-rank crystals.
Edit: and to answer OP, I would assume that T6A are considered "top tier rewards" and are therefore in the Jubilee crystals.
With the superior ones is the only way for the rare champ selector or founders key from the jubilant crystal? Otherwise weird they are in greater but not superior