poor replacement for the older remote app.
The remote widget in Control Center does almost everything the Remote app did, and then some more.
There is no microphone feature
Yes there is. Use the standard Siri button for your device to activate it, when the widget is active. On newer iPhones, that would be the side button on the right. The start screen even shows that.
Text input fields will show an additional microphone icon for dictation.
Volume is useless since it can not connect to volume control of tv or Sonos or any other audio system on the WiFi.
Just like the former app, Volume Control through the software remote is limited to Bluetooth speakers and AirPlay speakers, and it may also support certain AV receivers that support Volume Control over HDMI-CEC.
Your iPhone or iPad will of course not send IR signals to your TV or Sonos, as the iPhone or iPad has no IR transmitter built-in, different from the physical remote.
Channel does nothing since the menu button is how you change between apps.
The new Channel Up and Down buttons are for TV provider apps that have chosen to support these buttons within their app. Similar for the Guide button top-center. I think Spectrum is one of those live TV providers that has an app with ordered in-app channels that can use this feature.
Control Apple TV with iOS or iPadOS Control Center - Apple Support
Set up the Apple TV Remote on your iPhone, iPad, or iPod touch - Apple Support
Use buttons on the Apple TV Remote on iPhone - Apple Support
If you have additional comments for Apple, then please use the feedback form. Feedback - Apple TV - Apple