Sensual Pleasures and their removal (MN 19 & MN 75)

MN8 Self-Effacement actually discourages focusing on Pīti and warns that it is not an objective in itself. Instead, the training and the path require a broader consideration.

It’s possible that a certain mendicant, quite secluded from sensual pleasures, secluded from unskillful qualities, might enter and remain in the first absorption, which has the rapture and bliss born of seclusion, while placing the mind and keeping it connected. (...vivekajaṃ pītisukhaṃ...) ... But in the training of the noble one these are not called ‘self-effacement’

With delight being the root of suffering, sensual pleasures are bound up with identity and craving. Attenuation of sensual pleasure (i.e., "This is not mine, etc.") is accomplished by long, steady effort of mindfulness, the relinquishing of the fetters, the Noble Eight-Fold Path. Experiencing piti during meditation helps establish mindfulness during meditation. However, that meditation mindfulness must be maintained and developed in all aspects of life. Applying that mindfulness every moment is what attenuates sensual pleasure.

For a discussion on the definition of mindfulness, MN10 Mindfulness Meditation is an excellent source

According to these suttas, is it somewhat possible through seeing the inherent harm in sensual pleasures, to shy away from them?

These suttas seem to me to imply that sensual pleasures are impermanent and dissatisfactory, rather than directly harmful (though presumably addictions and so on can be harmful too).

These suttas are addressed to monks (MN 19) and a wanderer (MN 75), so I suppose that their ethics were already in place, that the audience had already self-selected life as a recluse, and so with them it wasn't a matter of actual outright harm.

This is why I believed that piti is then the "so to speak" new drug for feeling pleasure

I think that MN 19 and MN 75 both describe the same sequence, i.e.:

1. Stop chasing sensual pleasure
2. Find immersion
3. Find joy or bliss

So if you're hoping for piti to replace sensual pleasure, it may not work like that -- perhaps, on the contrary, bliss is the non-chasing.

I was reading DN 16 again recently:

Oh! Conditions are impermanent,
“Aniccā vata saṅkhārā,

their nature is to rise and fall;
uppādavayadhammino;

having arisen, they cease;
Uppajjitvā nirujjhanti,

their stilling is true bliss.”
tesaṃ vūpasamo sukho”ti.

MN 75 says,

Take someone who used to amuse themselves with sights known by the eye that are likable, desirable, agreeable, pleasant, sensual, and arousing. some time later—having truly understood the origin, ending, gratification, drawback, and escape of sights, and having given up craving and dispelling passion for sights—they would live rid of thirst, their mind peaceful inside.

I remember that it by first experiencing piti during meditation that one slowly but surely starts to abandon sensual pleasures

Instead, abandoning sensual pleasures is a prerequisite to meditation, and piti is a result (and so, not something you can count on or wait for as a cause).

This essay seems to agree with you somewhat (about replacing one thing with another):

For example, if you're addicted to alcohol, it's not because you feel that the alcohol has any inherent existence. It's because, in your calculation, the immediate pleasure derived from the alcohol outweighs the long-term damage it's doing to your life. This is a general principle: attachment and addiction are not metaphysical problems. They're tactical ones. We're attached to things and actions, not because of what we think they are, but because of what we think they can do for our happiness. If we keep overestimating the pleasure and underestimating the pain they bring, we stay attached to them regardless of what, in an ultimate sense, we understand them to be.

Because the problem is tactical, the solution has to be tactical as well. The cure for addiction and attachment lies in retraining your imagination and your intentions through expanding your sense of the power of your actions and the possible happiness you can achieve. This means learning to become more honest and sensitive to your actions and their consequences, at the same time allowing yourself to imagine and master alternative routes to greater happiness with fewer drawbacks. Metaphysical views may sometimes enter into the equation, but at most they're only secondary. Many times they're irrelevant. Even if you were to see the alcohol and its pleasure as lacking inherent existence, you'd still go for the pleasure as long as you saw it as outweighing the damage.

I get the impression though that the suttas aren't saying, "try seclusion instead of sensuality, motivated by piti!" -- instead I think they talk about e.g. nibidda as the motive.

Still, it says "alternative routes to greater happiness with fewer drawbacks" -- maybe you're emphasising "greater happiness", and me, "fewer drawbacks".

I guess a problem is that chasing greater happiness might be another symptom of the same root[s].

Seeing the danger of sensual pleasure is actually one of the five strategies in the next sutta - MN 20. Obviously sensual pleasure is very difficult to abandon and one'd need to take a comprehensive approach that involves all 3 gateways of Sila, Samadhi, and Panna to have a chance of success.

There is a sutta where the Buddha says that until he experienced piti during meditation; his mind was still capable of returning to thoughts of sensual pleasure.

This said, starting the path requires abandoning sensual pleasures before experiencing piti. The Buddha abandoned sensual pleasures well before his development of the 1st jhana.

The mind that never thinks of sensual pleasures is a non-returner yet the eightfold path for mere stream-enterers has the abandoning of sensual pleasures as its 2nd and 6th factor.

Believing the 1st jhana must be attained before abandoning sensual pleasures is wrong view.