Updated:  Original post was TLDR.

Long and the short, my two boys got Beyblade Burst for Xmas.  They got a stadium that came with Hasbro Kerbeus K2 and Valtryek V2, along with these avatar things.

Even though Kerbeus seems to outclass Val and is easy to use, the youngest insists on Val.  I found out he also likes Xcalius, Kerbeus (to a lesser extent) Doomscizor, and Zeutron.

What do we need to make Val more competitive with Kerbeus, or is there a good, simple to use Bey out of box?

I've just been binging information on Beyblade the last couple weeks as a way to bond with my nephews. So far I've only gone for the Takara Tomy beys since they release on a sooner interval, however they come with a premium pricing.

I think from hasbro and those that you've listed Xcalius X2 is a pretty legit choice. It's an attack type like Val and from some videos I saw hits pretty dam hard with its pointed sword tip. I'm considering grabbing one for myself(TT ofc)

Spryzen is also a pretty cool Bey to get a hold of. The Bey belongs to a popular hero on the show as well(behind Valt obviously) so I think your kids would attach to it at least as much as they do Valtryek/Valt. Spryzen S2 is out now, but rumor has it that the revamped version is coming out Jan/Feb of this year. If not, the Spryzen 2 is plenty good in its own right.

I haven't gotten to Zeutron b/c I haven't seen him in the anime yet. He looks great though aesthetically speaking.