Pleasure is happiness. If you could afford it you can have great food, unlimited sex, free time to pursue passions and interests and most importantly endless, unrestricted power over people all the time. The above, combined with no stressors will pretty much guarantee life long happiness.
The only caveats are drugs (generally destructive) and clinical depression caused by hormonal imbalances.
Pleasure is immediate, whereas happiness (or joy) reflects something more long-lasting and is often ineffable.
You can get used to pleasure because you can predict it and control it. Joy and wisdom are not gained so easily, and it's that challenge that creates meaning.
If you had a brain scan of pleasure and a brain scan of happiness, do you think they'd be identical?
I think you understand that unbridled pleasure eventually leads to jadedness, because you excluded drugs. The other forms of pure pleasure do the same thing but over a longer timescale. Yes, you'd have a truly amazing time at first. Why do a lot of rich people turn to drugs or gambling?
The only caveats are drugs (generally destructive) and clinical depression caused by hormonal imbalances.