Some define like that
because they don't have the experience.
If I tell you
'Fire burns'
it is a truth which is timeless - eternal is the right word.
if you stop at there
preserving it as knowledge.
If you test it
'fire burns'
instantly.
in NO time.
A+Kalika.
The moment one starts
walking on the path of dhamma
experientially
suffering starts decreasing
in NO time..
Akalika.
But can one develop only Seela and Samadhi without Pragna ?
If one walks on Buddha's path
all 3 develops simultaneosely.
Lincoln may not have heard of Buddha,
but he walked on the path.
If one is aware with Upeksha,
if one try to be aware of everything
he develops all these 3
and he is already on the path.
I think you too are
on the path
or very close to the path.
The questions you ask
are of a seeker... not of a believer.
These are the 3 type of Buddhas. To attain Nirvana, one doesnt have to be a Buddha right ?
One has tobe one of the 3 Buddhas.
By reaching the state of Arahath, you will attained Nirvana at your death wont you ?
One attains Nirvana
at the enlightenment,
and lives in the state
of
Sampajano Sati.
In Sampajano sati he is aware of everything he perceives effortlessly
because no sankhara to mislead him.
All the Sankharas eradicated
no new sankharas will be formed.
No attachment left.
(Visankhara gatan chittan Thanhanan khaya majjaga....)
But as long as body lasts he will live
in the state of Nirvana.
At the death
he attains Parinirvana.
Nirvana is complete.