I would direct you to the highlights of his matches at the Shanghai Masters 2016 which was the last ATP tournament he competed in.
Rafa continues to use the buggy whip technique on many of his FH shots regardless of where he is aiming them in the court.
If you're saying that playing with heavier racquet is no more taxing on a player than playing with a lighter one, especially one that the player has used for many years, well perhaps we can agree to disagree. (Also, there is no point comparing players in this regard because every player is physically different. )
In any case, there is no doubt that equipment can enhance or detract an elite level player's performance. It will be interesting to see what changes Rafa does make, if any. And if he does make changes, it will be interesting to see what impact it has on his performance.
Nadal in defensive mode like against Troicki where he was pushed back from the first ball he definitely uses the heli style (bw)
and loses as he has of late against aggressors.
In this recent vid practicing with head like racquet you can see he only goes for the BW on a low short ball otherwise across the torso every time.
When Rafa is confident he employs the Fed style follow through but reverts back to heli BW when hard pressed eg. Shaghai.
You can see when he is confident and dominating he rarely uses the defensive over-spinning defensive BW FH.
As for heavier sticks not being taxing its all within very important dynamic limits of course. For example anything around 340-380gsm
seems to be no problems at all for a player like Nadal, Novak, Murray and Federer and Novak has alot of work on that FH with quite
amazing head speed as does Federer while Murray is more compact and efficient on that side when taking it early.
Jack Sock also with a stock 343 + 6-8gsm overgrip uses a BW FH that often lands short regardless of his heavier arm yet lets
him down in consistency which is no issue while he is younger than Nadal and bigger framed but for Nadal this style is too taxing
and also less effective vs all BHs in the game today. He clearly knows he needs more penetration and counter-punching control
and that is by compromising the no longer effective overuse of zizzling spin rpm but increase the weight of shot with accuracy.
This recent clip illustrates that Nadal often practices like a Bull with a Fed like finish as he is full of confidence, yet he changes
to using the Heli (or for USA terminology buggy whip eg. BW) only on crosscourt and late shots as opponents usually
play more offensive than he does so he weathers the storm till he can pounce. However that no longer works for him today.
Nadal when on offense has equally as devastating as Novak with flatter shots however the lack of weight
creates more issues in overall control vs that of Novak, Fed and Murray which Murray especially now
destroying Nadal on his beloved Clay with more solid on the rise offense than Nadal could handle.
There is a fine line but even myself with a similar open stance BW FH since 1977 (regardless of what my coaches tried to change me)
have no issues and find a huge advantage going from 346-376gsm for 3-4 hours matches vs 20 year younger kids.
Even one of my 55kg 182cm young charges after going from 290 to 320gsm now 356gsm and complaining initially it was too heavy
he now is a different beast with more accuracy with depth and would never go back