The English translation using "was" is neither here nor there: that's just an auxiliary verb we use to make past tenses.
But a similar question arises in the original language.
Joseph Blenkinsopp writes at length about it in 'Creation, Un-Creation, Re-Creation, 2010'
p.30:-
By construing the opening sentence as a main clause rather than a
subordinate temporal clause, this version provided warrant for a
theology of creation from nothing (creatio ex nihilo) , the standard
and orthodox theological understanding of creation in early Judaism
and Christianity. Creation out of nothing can be argued on
philosophical and theological grounds, it was accepted in Judaism
before Christianity (see e.g. 2 Macc. 7:28 where it is explicitly
stated), and if not explicitly formulated in the New Testament is
hinted at indirectly (Rom. 4:17; 1Cor. 1:28; Heb 11:3). All this
notwithstanding, it has been known at least from the Middle Ages - for
example in the commentary of the Jewish scholar Rashi - that from the
linguistical and exegetical point of view this reading of Gen 1:1-2 is
not the preferred option in strictly exegetical terms.
He advances a second argument: that in the history-of-ideas (i) Gods don't necessarily create ex nihilo - e.g. in the Enuma Elish they only appear on line 8 and (ii) they sometimes have to contend with chaotic forces.
There is a third argument: that some pre-Christian Jewish texts have different sequences of creation - e.g. Wisdom being created first in Prov. 8:22-31.
The LORD possessed me at the beginning of his work, the first of his
acts of old.
His best argument though, I think is in a different book (maybe 'Genesis: A Commentary'?): that the second word of the bible בָּרָ֣א=bara can't mean to create ex nihilo - since it's also used for the creation of humanity (Gen 1:27-28). In the sense of make/shape/create it's only used of God. Of humans it's used for (e.g.) clearing a forest (Joshua 17:15) and making someone fat with offerings (1 Samuel 2:29).
How Blenkinsopp would answer the OP I think is on p.32 - the pre-existing material was the 'shapeless mass'='tohu wabohu' occupying the space between the upper waters and the lower waters.