Do we now want to +10 Fjorm?

A summoner can only dream,+10 a fjrom?that's to costly.

It's an optimal decision. It should cost around 900 orbs which you can do if you save up. Her base kit scores well enough so all she needs is a dual rally and a 240SP Seal like DD3 or QR3.

For people really into arena scoring, it is highly recommended. Akariss knows the ins and outs of how it works; I'm not familiar with the details.

Scores are consistently higher during water seasons, and I cannot think that Fjorm merging isn't a significant part of it.

Having a Legendary Hero on your team will boost your score by 2 points for each Hero you have Blessed that have the same attribute as the Legendary Hero. You can get up to +6 score for free per battle by running a team full of Water-Blessed Heroes and a Water Legendary Hero during Water Season. (This, of course, applies to all the Blessing types and Legendary Heroes.)

Fjorm merges are going to be important in the future, as more and more people become serious about Arena and Arena Assault scoring. I'd go as far as trying to get +10 merges on at one Legendary Hero of each type to guarantee bonuses for every season, then saving up to three of each type of Blessing to change your other two units + Arena bonus each time the seasons change, but I realize that this will be very difficult and impractical for a majority of the players.