As with everyone else what oil you want to put in your engine and what oil believes you want to accept and reject is up to you but you have taken on the popular beliefs but that doesn't mean they are correct.
Just to give you a bit of background the British engines in my British "classics" from the 1960s and 1970s were first built in the late 1940s and early 1950s (that one went on until the new century, year 2000, with some minor updating at the start of the 1980s). These engines were 8v, OHV. I have been driving cars with these engine since 1977, I wouldn't be able to guess how many miles but a lot and not usually slowly.
The (proper) Mini that had the A-series engine and shared gearbox was what promoted the use of the early multigrade (20w50) engine oils in the UK at least.
In the 1990s I used the contemporary Mobil 1 15W-50 in my cars with those engines and the common wisdom was that the oil would ruin the engines (rot my teeth and steal my looks) usually by old-farts with "classics" that they very rare drove and then like a maiden aunt going to Sunday afternoon tea as they thought the cars would fall apart if driven as they were designed to be. Those engines were fine and performed well and I put many tens of thousands of miles on them the few years I owned them (and I have kept all my teeth (including a baby tooth still in my jaw) and my looks).
ZDDP is a useful marketing tool to sell special "classic" engine oils at higher prices for an older oil that should be less expensive, in the UK at least, if want ZDDPs it is the whole additive package that matter more than one ingredient - and then how many ZDDPs is required? Having researched this a bit I have never found a figure for ZDDPs (usually shown as ppm - part per million) for the multigrade 20w-50 popular engine oils in the UK in 1960s nearest I could find was perhaps 600 or 900 or in between yet when I last debated this the "specialist" "classic" car engine oil with ZDDP in bigger letters had IIRC something like 1300 ppm. Now apart from 900 being the highest figure I saw for 1960s as I put before wear protection is given by a range of additives in the additive package.
Found this table for API grades of maximum zinc (I don't know if it's correct).
SM 800 zinc
SF-SL 1000 - 1400 zinc
SC-SE 1000 - 1200 zinc
SB 1000 zinc
SA 0 zinc
I have no idea what caused your wear, perhaps too little zinc in an unsuitable additive packages to the engine oils used might have contributed, perhaps not, depends on the particular oils used in your engine in your driving conditions from when the engine was first built (or rebuilt).
I am a bit confused why you have chosen a diesel oil and then used API for petrol engine, plus what makes SJ suitable for OHV and not later specs, the link you put up goes to at least SM for backwards compatibility. ETA: just thought diesel may have higher zinc levels(?), I have never looked at diesel engine oils specifically.
For your Mobil diesel oil heavy duty means in chisel trucks, mining, quarrying and agricultural industries which I suggest would involve far more heavy-duty loads than your car could ever take - "Mobil Delvac Legend 15W-40 Heavy Duty is recommended by ExxonMobil for use in a wide range of heavy-duty applications and operating environments found in the trucking, mining, construction, quarrying and agricultural industries."
No specific to your car but when you have time have a look at these videos for general information regarding ZDDP and wear.
https://www.youtube.com/watch?v=Kg7edyYgD8E
https://www.youtube.com/watch?v=7AJ_DO5zfVE
https://www.youtube.com/watch?v=erxjPicpYyw
HTH.