Champions are SRD, and Mountaineers are mostly fine for a Strength+Athletics shield build, but Spellblades need some help being relevant compared to Rangers and Paladins. In a campaign with a stronger focus on out-of-combat abilities, they might be fine, but Solasta is mostly combat and a 3rd caster with Evocation, Enchantment, Conjuration and Transmutation spells have little they can offer. These schools aren't bad, but they are best used by more dedicated casters.
The simplest change I could suggest would be to give Spellblades access to the Abjuration or Illusion schools of magic to give them some in-combat defensive capabilities.
An alternate solution could be to give Spellblades a feature at level 3 or 7 that uses spellslots, but isn't a spell itself. Here are a couple of ideas:
Channel Arcana: Fire/Frost/Shock. Spellblade level 3 feature.
As a bonus action, you can spend a spellslot to give your weapon attacks +1d4 fire/cold/lightning damage for 1 minute.
Channel Arcana: Bulwark. Spellblade level 3 feature.
As an action, you can spend a spellslot to give yourself a bonus to AC equal to your intelligence modifier (minimum of 1) for 1 minute or until you lose concentration as if you were concentrating on a spell.
Typos happen. More so on the phone.