Worked on friend’s bike. Now kinda wishing I hadn’t…

I’ve been diagnosing a friend’s bike (Specialized Ruby Elite, 105), after I replaced a badly-worn chain (it was at 1%). Her LBS say they swapped the chain 1800 miles ago. The wear I found at 1% says to me that’s more like 6-7000 miles on that chain (Tiagra HG4601, correctly-oriented with writing on the outside, jointing pin in leading hole of plate, no link binding).

Also they say that they replaced the 105 5700 cogset (11-28T) – but the new chain now skips under heavy load on *all* cogs, not just the smallest few. So I doubt that got swapped either. And on the invoice it showed a new 105 BB5700 (not fitted, still the OEM Ultegra BBR60 on it), BBB jockey wheels (rear mech has the OEM Shimano ones still). Dodgy?

Looking at the cogs, the teeth have burrs on them commensurate with 6-7000 miles, comparing with a now-retired Tiagra cogset of mine the same age.

Hanger alignment, rear mech alignment, indexing are all fine (I did all-new cables).

Leonard Zinn (yes that Leonard Zinn) confirmed that a very badly-worn 11-28T cogset might skip on the larger cogs as well as the smaller ones if knackered enough. I’m used to seeing skipping on smaller ones due to the reduced diameter/fewer links engaged, this is the first time I’ve seen skipping on all of them.

I replaced the cogset and she took it for a 100-miler. So that’s new freehub/bearings (the original fault), new 5700 cogset, new HG4601 chain, BB has no play in it, indexing fine – but it’s still skipping under heavy load in all cogs, both rings. ~X(

So now I think the next step / likely / only cause remaining is the chainset.

Correct? anything else any can think of?

I did the ‘lift test’ and could only clear half a tooth at the front of the big ring with the new 10spd chain on – I’m used to thinking a chainring is OK until you can clear a whole tooth. Am I wrong?

To add insult to 5-6hrs of my time gone so far, she took it to a TT tonight whereupon a bunch of blokes proffered their thoughts and pronounced my handiwork shite.

What started out as replacing a shot freehub with wasted bearing faces has turned into an introspective should-I -give-up-bike-repairing-forever funnel of despair.

Thoughts very much appreciated.