In classical propositional and first order predicate logic, they are equivalent as you noted by the truth table method. In classical FOL, 'and' and 'or' are dual (for every theorem with an 'and' there is a corresponding theorem where it is replaced by 'or' (and other things are rearranged accordingly.
As to necessity, well, one can redefine anything, but then you might be talking about something different, and one can doubt anything, but doubting doesn't make something true or false.
Which is to say... 'or' is considered a little more nuanced than 'and'. One can imagine certain circumstances where one is not so sure of 'P or -P'. For example, in the intuitionist judgement of the normality of pi), there is the idea that one can't really know one way or the other if every possible finite subsequence of digits occurs in the infinite sequence of digits of pi.
There is large amount of study of logics where 'P or -P' is not a theorem (not that it is false everywhere or even false once but simply that it is not provable in that system).
On the other hand, no one really bothers trying to doubt 'and'/LNC, because you don't have a very useful proof system without it. As an intellectual exercise one could deny LNC, but that little machine doesn't do too much. In contrast, one can still do lots of interesting mathematics while denying LEM (to be clear, when denying LEM, you're not using classical FOL anymore).
In the end, 'or' has the slightest bit of extra doubt to it than 'and', so LNC is pretty indispensable, but the lack of LEM doesn't make everything fall apart.