Of course it isn't! Those who want perfect happiness, along with those who want freedom from all suffering, are seeking Nirvana, not Heaven.
Nirvana being just that: a place of unchanging bliss, in which time is not a factor and nothing happens. (Or, at least, we are conscious-of nothing happening.)
Nirvana is, therefore, a place in which the self, the person, awareness of individuality, is lost. Because there can be no awareness of oneself if perfect happiness and absolute freedom from suffering is required.
In Nirvana the individual is dissolved-into impersonal deity; experienced as a changeless state of simple being.
Heaven is altogether a different kind of place. It is a place chosen (as a permanent commitment) by those who wish to join the Good side in the spiritual war; it is the place where all participate in God's work of loving creation; it is a place of activity - in which motivations are Good, and all the inhabitants pursue these goals in harmony.
In harmony - yes; but harmony is more a matter of sharing (forever) a common goal, and dynamic harmony requires dissonance as well as resolution. Heaven is an endless, developing symphony; it is not a single chord (no matter how sweet that chord may be).
Creation is dynamic and entails change, love is dynamic and happens between individual persons (God is a person, Jesus is a person, the inhabitants of Heaven are persons).
If loving-creation is the primary and eternal aim of Heaven, then max-happiness/min-suffering cannot also be primary.
One source of sub-optimal happiness would be that some persons whom we love will not choose Heaven; we will be saddened by their absence, at least to some degree. We would prefer that they had chosen Heaven, but they did not. Our situation is by-that-much sub-optimal.
Another source of sub-optimal happiness is unrequited love. Especially when it comes to eternal spiritual marriage, it may well happen that our specific love for another specific person, and our desire to form a permanent dyad with them, is not requited.
Over the long term, presumably; adjustments are made and a better pairing emerges; but at least in the short term, it seems inevitable that happiness would be sub-optimal if we wish to marry another who does not wish to marry us - at least not for eternity.
In other words, the idea of Heaven as a place of perfect (= absolute and unvarying) happiness is a red-herring, a confusion, a case of mistaken-identity; or even a rejection of the actuality of Heaven and a preference for Nirvana.