In my area, there are almost no Standard RCs to even prepare for, with a majority of tournaments being Limited, or another format entirely
Rather, the effect making it an Aura ends, it loses enchant creature, and it remains on the battlefield as an enchantment creature
In the case of Urza, having him along with The Mightstone and Weakstone in play costs 8 mana total, not to mention the additional 7 mana to activate Urzas melding ability
Removing key pieces at the right time is crucial, and games can play out very differently, depending on which action (questing or challenging) each player focuses on - though you'll need to engage in at least a bit of both
For example, Urza will not just have the Urza, Lord Protector we already saw, but also Urza, Prince of Kroog in his younger days, and Urza, Powerstone Prodigy from his childhood