I suppose it all comes down to how much credence you give to the timeline given in the World of Thedas. What is the point of having a source book if you can't at least given some validity to what is contained there. Accord to WoT Arlathan was founded some 3000 years before the arrival of humans in Thedas and this is well before any recorded history so difficult to pinpoint the exact time. However, an alternative calendar has it being founded some 3000 years before the first contact with dwarves and around 4500 years before the first contact with humans. So clearly the elves were around for a long time without any humans.
If we assume the first contact with dwarves was connected to the war with the Titans, then this was some time before the appearance of humans. Both the timeline and the calendar have the humans first appearing some 1500 years after the contact with dwarves. If the war that Solas talks about that gave rise to the evanuris as generals, leaders, kings and finally gods, was the battle with the Titans, then that gives you a fix with regard to them.
Abelas talks about humans falling on the corpse of the elven empire but that doesn't mean there were no humans around before this occurred, simply they weren't strong enough to threaten the elves. Also there are two separate events, many years apart, concerning the rise of the humans. The first contact between the old gods and the Neromenian dreamers was only some 300 years after the first arrival of humans in Thedas. What is odd about this is that if Solas had raised the Veil only a few years before, it seems strange that the human mages were now more sensitive to speakers from the Fade rather than less. So it seems to me that shutting away the evanuris allowed these other "gods" to interact freely with the world, having previously been prevented from doing so. Since the old gods were imprisoned on the material side of the Veil, then I suppose this makes sense as the magic that kept them from being heard had been muted.
However, the final destruction of Arlathan by the Tevinter Imperium wasn't for another 1900 years. I'm surprised that Abelas would even be aware of this considering much of the time he was napping in Uthenera down in the Arbor Wilds, whilst Arlathan Forest was up in northern Tevinter. So whatever Abelas was talking about had to have been connected with the earlier time just after the raising of the Veil, when the elves were confused and leaderless and the realms of the evanuris in chaos. Dorian says the pictures of the dreamers with foci (orbs) was depicting a pre-Tevinter period, so it would seem that the Neromenian dreamers took advantage of the chaos to step in and steal a number of elven artefacts and this helped their rise to power as much as their use of blood magic did. My own personal theory is that these early humans had mated (raped) elf women they came across and the resulting elf blooded children were the first dreamers, which is why the old bloodlines of the dreamers were considered superior in later Tevinter. Elves, like mages, have magic in the blood and are preferred for use in magical experiment and blood sacrifice over standard humans.
Whatever the case, it seems highly unlikely that humans came about as a result of the raising/strengthening of the Veil by Solas but the events surrounding this event may well have given rise to the first human mages.