If someone steals your phone all they have to do so you won't find it is to wrap it in aluminium foil.
For a while now to steal a phone you needed a fence. The fence will just give you a metallised bag and you'll put the phone in it. It's not really more complicated than turning off the phone as thieves already do.
As for the software features, they've always been and will always be bypassable. People figure out how to defeat iCloud Lock, how to change ESN/IMEI/IMSI already. It's easily a 30 million dollar market, people will continue to figure it out.
it's another hassel for thieves which imho is a good thing. Might as well argue "why lock you door when all someone needs is a bump key!"
The only difference is now instead of turning off the phones they'll put it in a metallized plastic bag.
Also huh you finally gave me a reason why apple may be locking its hardware components now.
Thieves and fences always figure out how to bypass the component lockdowns.