I used to rely too much on the instruments, and got a boll*cking from an examiner and failed my SE CPL first time becasue of it. So I went out with a FI who covered all instruments except oil pressure and oil temp, and we used to go out and do all of the usual manouvres, steep turns, stalls, lazy-8's chandelles totally instrumentless. We even progressed to flying back into the circuit using just rudder and trim (no instruments still) and put the aircraft in a position to land..........Didn't land it without elevator due to insurance and the risk of breaking someone elses plane, but reckon I'd have done it ok.
I learned a lot, and although a bit disconcerting to start with, you get the feel pretty quick.
The problem is recognising instrument failures. Its all very well to say "you should do this" or "you should do that" but if say the ASI is giving false readings and you don't realise it, you're in big trouble. As happened to a 727 (I think) in the USA some years ago. ASI failed in the climb, so they kept pitching up to *reduce* airspeed and eventually when the stick shaker started, they realised what had happened. They stalled, and crashed, killing everyone.
Its easy for us to say "They should have clicked that something was wrong as the airspeed was rising even though they were pitching more and more up". Still they didn't realise, and paid for it................