Three weeks ago I remembered that my erratic shifting might be due to the fact that I was using Tacx jockey wheels. In a previous attempt to eliminate noise I had changed jockeys. It is a strange anomaly that all aftermarket jockey wheels use cartridge bearings, and none that I have seen have a floating guide wheel which Shimano derailleurs do need. So I put the XT jockeys back in the cage and shifting returned to smooth precision.
Two weeks ago I sprinted to get through a short green light, and after that I could not shift past half the cassette. The b-spring broke, cementing the fact that my modification was not a viable solution. It lasted around 1400 km (granted, it was an old and second-hand derailleur).
I promptly ordered a Tiagra 4600 SS derailleur and a Wolftooth Road Link, as this combination is (according to Wolftooth) going to work out of the box. Assembly took a whole 5 minutes, including shortening the chain to Shimano/Sheldon Brown’s 2 full link overlap sizing. Contrary to Wolftooth’s directions I was forced to screw the b-tension screw in fully, else the chain would have no tension on it in smaller sprockets. Also, after dropping the chain a couple of times, I had to adjust the derailleur’s a-pivot to the tighter setting.
The Road Link does what it says it will do, however shifting is not perfect. I think this is a better solution to modifying a derailleur, however it is still not as robust as a native wide-range 1x drivetrain. I am looking forward to trying SRAM with a similar setup.