Originally Posted by
sophontteks
The additional effort is that you are using your action to cast the spell in opposition to doing something else. The idea that an action must be spent doing something every round is only relevant during combat and its pure meta knowledge anyway. Rounds only exist for the ease of running combat mechanics and don't exist in RP. Without any movements or sounds during the casting I have no idea what the deception roll is hiding. Your decision is running in opposition to the abilities effects; deception check must be rolled to hide the tells the ability explicitly removes.
From the characters perspective there are no rounds. Everything is played in realtime. Characters are not remaining still while casting a spell, they have free movement and the ability to continue reacting to their environment, including dodging and parrying attacks. The concentration involved in an "action" isn't very limiting. Wizards aren't going through some form of mental constipation when they cast a spell. Its very fluid and happens within 6 seconds or less.
In addition, look what sorcerers give up to have their metamagics: very limited spells, loss of other useful metamagics, using a very limited long-rest resource. You are nerfing them very hard and I doubt many players would be pleased to build a subtle caster under these conditions.