You get a guaranteed SR from the 3rd panel prize, and you'd have to be truly unlucky to get none from the first two jewel gacha pulls. It's of course possible, but super unlikely. Plus of course the 4 guaranteed SRs that you get just from regular quest progression (Nike, Amon, Cybele and Baal).
I'm not saying everyone's going to pull a Sol+Tyr every time, but you can clearly put together a workable team even if you just used whatever the game gives you and slot in Nike as a healer in a pinch.
That's all I was trying to get across up there. I reroll constantly, but I dont hold out for multiple SSRs when I'm just trying something out. Any two SRs in the same element are usually enough for me, and I didn't even have that on my first account. Beelzebub carried that team on her back all the way through the first event, even with no decent Eidolon that you couldn't get from Material exchange, and that team is only slightly weaker than my Amon+Tyr death squad.
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Ugh, I just lost my previous reply somewhere so this one's gonna be a bit brief.
http://xn--hckqz0e9cygq471ahu9b.xn--...83%96%E3%83%96
Basically, your first Legendary Soul is important from a time/effort standpoint, but nowhere near a huge deal. Whatever garbage Gacha-sama blesses you with is more than enough to clear Raids and Events as long as you put in some effort farming to highlight their strengths, but you'll always be able to get to a point where you can solo Expert and get that weapon grid filled out within a week. Which means you can farm the Expert level Events (for the near future), which means you can always hit some tier of viable while maintaining your free player status.
By the time harder content rolls around you'll be able to unlock a second or third Legendary Soul, and you'll have a much better idea of what works with what you've been given. But the ceiling on what's possible with what you have isn't going to change a whole hell of a lot based on which Legendary you pick first, as it's really just a matter of having enough health not to die while you wait for your healer's cooldown at the moment.