This is a difficult question to answer because it is very broad. Your sources concern a number of different pathologies which have different mechanisms and different treatment approaches.
It's important to differentiate between acute and chronic pain because chronic pain is not associated with continued damage to the tissues. This means that e.g. whether NSAIDs inhibit the immune system from contributing to healing may not be relevant to chronic pain where the initial insult has disappeared.
Back pain can be an acute musculoskeletal injury or chronic pain which is no longer associated with damage. It may also be musculoskeletal vs neuropathic which may have different management.
Your sources move between several levels of evidence from in vitro experiments to Cochrane reviews. In terms of evaluating the quality of evidence for current treatments it is probably better to stick to systematic reviews so I will use Cochrane from here. I will also restrict my answer to NSAIDs and paracetamol in reference to non-neuropathic back pain.
The short answer is that the evidence for any treatment isn't great, and the results are contradictory even when taking large numbers of studies in aggregate.
The review authors conclude that NSAIDs are slightly effective for short-term symptomatic relief in patients with acute and chronic low-back pain without sciatica (pain and tingling radiating down the leg). In patients with acute sciatica, no difference in effect between NSAIDs and placebo was found.
The review authors also found that NSAIDs are not more effective than other drugs (paracetamol/acetaminophen, narcotic analgesics, and muscle relaxants). Placebo and paracetamol/acetaminophen had fewer side effects than NSAIDs, though the latter has fewer side effects than muscle relaxants and narcotic analgesics.
Only 42% of the studies were considered to be of high quality. Many of the studies had small numbers of patients, which limits the ability to detect differences between the NSAID and the control group. There are few data on long term results and long-term side effects.
So, NSAIDs might help a bit in the short term.
We found high-quality evidence that paracetamol (4 g per day) is no better than placebo for relieving acute LBP in either the short or longer term. It also worked no better than placebo on the other aspects studied, such as quality of life and sleep quality. About one in five people reported side effects, though few were serious, and there was no difference between intervention and control groups. As most of the participants studied were middle-aged, we cannot be sure that the findings would be the same for other age groups.
So paracetamol (i.e. acetaminophen) is probably not ideal. This is confusing in relation to NSAIDs being found to be no better than paracetamol but still effective.
In practice
The current UK NICE guidelines for management of low back pain are basically:
- Rule out any "red flag" pathology
- Identify any underlying cause. If back pain is secondary to a treatable cause e.g. osteoporosis then that should be dealt with first.
- Provide information on exercises for low back pain
- The current guidelines then suggest to offer NSAIDs, and if these are not tolerated to offer codeine. These are both given for the shortest possible time at the lowest dose that relieves symptoms.
This is probably based on that on balance NSAIDs are probably the least worst choice although it would be fair to conclude we are still not very good at treating this condition.
