Yes and no.
For the same distance between you and subject, then yes, its equivalent to a 90mm FOV.
For light gathering, no, its f1.8
For DOF, for the same field of view, then yes, DOF is equivalent to f3.6
Whether this is important to you or not, depends on the genre and style you shoot.
As a rough an example, to get a full body shot with the 45/1.8 on m4/3, you need to stand 12m away. (can be a tad tougher with ppl milling about in betwwen you and subject)
You'd also get the equivalent f3.6 DOF in terms of subject isolation.
On a FF camera with 45/2.8 lens, you'd only stand 6m for that same full body shot with a f2.8 DOF
Some folks don't shoot that much for isolation, in which case, all this does not matter.
In my case, I have used m4/3, aps-c, FF (and compacts).
I never lament at what I have and what I am using.
I just frame with the focal length I have at hand for what it can give.
But then, its really an individual thing/preference.