RED studio makes strides in card pool balance. But it's time to balance the leaders ! I believe at least three leaders in each faction should be playable !
Mystic Echo: Play a Scoia special card from your deck. Reason: double best special card is too strong move.
Pincer maneuver - flip ability: Play a card from your hand, then draw any Northern Realms faction card. Reason: drawing any card is too strong move.
Read some good ideas here like make it tutor a special card so you can't play your best one twice and set a provision cap for it.
Personally I would like for leaders to not be played in the same turn as a card from hand. This would solve a lot of the combos in Homecoming that have been considered broken (Dijkstra Townsfolk, Mystic Echo, pincer maneuver etc.)
You'd still be able to get strong combos off but equally your opponent gets an honest chance to counter. An immediate obstacle is the fact abilities like Meves' and Brouvers' exist. But honestly for all I care they can be reworked to have a powerful single use ability anyway as I personally prefer those (would also make Arena mode more playable as many of these abilities are synergy based)
Then again a lot of people might appreciate them so I don't know. But I do think it would help a lot in terms of balancing and I don't think it would go at the expense of creativity or fun.
I don't like the idea of completly reworking something that works, but it's probably the only way for Gwent to become more balance-able. Those leaders you listed are causing endless problems. Even through i like most of them (+Doublecross), at this point i'd rather have balanced game. Mobilization is OK imo.
Francesca's Mystic Echo => Harmonic Resonance : Charge 3, Give one unit Harmony and trigger all friendly units with Harmony.
Should the ability be too Strong with Fran, it's possible to give it to Calveit, instead, using Assimilate. But it shouldn't be applied to all factions because that would make the leaders, once again, boring.