Saxon is another unit you get at the start of the game, so he naturally has great availability. Early on he is great about setting up kills or finishing off kills with his personal skill while his passive is never great but never terrible, healing him on a percentage of his max HP. With both Monk and Ascendant being really great classes and him performing well in them, I think that is good enough reason to earn his spot in B tier.
Early on, Saxon finds a lot of success in Monk, though Conduit is a viable option.
Monk - Here, Saxon enjoys having access to the Charged Ki skill. For a cost of 60, and a duration of 2 turns, he can keep this up 2/3 of the time. Early on, this allows him to beat the stat curve and punch through high defensive enemies like Trents. Additionally, simply just using the skill will heal him due to his passive.
Conduit - This class gives Saxon some alternative spells to use. Chain Lightning has a significantly different attack style than Call the Storm and it's damage doesn't get reduced. Additionally, you may find yourself using Defibrilate a lot more than you'd think in Demonic. The passive will boost his combat potential while also retaining his 1-2 range which is always nice.
Gale - is pretty mediocre. Ravager Winds is nice when you can get it to work and Stormborn is great early to have an answer to certain enemies, but the enemies in Demonic have too much accuracy to make this dodge tank class work. Additionally, 1 range holds it back even further.
Frigillan - Saxon doesn't have a great bulk and while there is merit for the Ice Spire and passive, there are just better alternatives in the game. Like the case with Gale, 1 range holds this class back even further.
Godfrost - In Godfrost, Saxon will have a slightly rougher time than Zuhair due to a little less fortitude and not being able to patch it completely, but can run a different Ring setup entirely. The Aqua Ring will increase the scaling of Absolute Zero and the Attuned Ring will let him cast it 3 times spanning 9 turns of increased defensive bulk.
Ascendant - In Ascendant, Saxon retains his decent Mastery but also has pretty respectable stats in everything but luck. With Divine Flow making it where he can't be hit by anything besides an enemy with the empowered guaranteed to hit trait, he will stay at 100% hp pretty reliably. Divine Flow also stacks on itself. The idea is to tank enemies with Divine Flow, finish them off with your team and repeat. With this setup, Saxon should be getting 11 mana after every combat, assuming he can counter and double.
Stormkeeper - In Stormkeeper, you can opt for the Monk or Conduit dip. Personally, I like the Monk dip, just ensuring my stats are high. Conduit is another decent option, excelling in what the class wants to do - throw out spells.