House rule the spells immediately and tell him he should have known better. Maintaining Game Balance is EVERYONE's prerogative, not just the GM's. GM is just the one where the game breaker's buck stops at.
Ok - I am going to push back and defend this PC.
First, this is not a case of someone finding obscure rules and cobbling them together to Win the Game (tm). These are core rules and Powers, and the Powers are broad such that they encompass many of the spell concepts one sees in other fantasy games. Plus for those not familiar, Savage Worlds has some swing to it - there is no CR/XP "here is your encounter and you should survive with 25% of your resources expended, +/-2%." There are Bennies to mitigate that Swing for both the players and the GM. But there is not the pure "game balance" that most people think of when they think about D&D.
There is nothing egregious here.
What might help is if you post the character, including the progression. Savage Worlds does not have a true Dump Stat (tm), so everything has importance. Conceptually the player can either build a focused PC with some weaknesses or a broad PC with few weaknesses but is not as effective at any one thing. So to be a good warrior they need decent Strength (for damage), decent Agility, good Fighting, and solid Spirit and Vigor to take the shots. To be a good mage you need good Smarts, decent Spirit, and good Spellcasting skill, and Power Points. A good warrior picks up Edges that allows them to attack more targets, attack more often, or attack more in certain situations (First Strike, Counterstrike). A Mage picks up more Powers, more Power Points (to cast more spells), and Edges to help with spellcasting (Rapid Recharge).
So if this PC is blending the two, then they are sacrificing something to be able to pull it off. At Veteran I can have a Warrior type with Improved Frenzy which gives me an extra attack EVERY ROUND ALL THE TIME - no power points needed. Instead of have d8 in Spellcasting I could have a 2 or 3 dice higher in Fighting which increases my Parry 2 EVERY ROUND ALL THE TIME (plus I will get more Raises, so more damage as well). Instead of picking up Spellcasting and an extra Power , I could have taken Edges like Two Fisted and Ambidextrous - which would give a second-hand attack at no penalty EVERY ROUND ALL THE TIME. I could easily have a swashbuckling swordsman with d12 Fighting and three attacks around with no penalties.
This PC is exchanging all that for some flexibility but at a steep price. They have to cast the spells (risking Backlash twice in the same round - you are enforcing Backlash, aren't you?). They have to spend a whole round doing this - using up 1 of the 3 "free" rounds of this (and using up 6 PPs to active). He has this going for 2 rounds then has to Maintain - that's 3PP per round and -2 to any other Arcane Skill check he decides to do (cast another spell). Then there is Disruption - if he takes damage (including Shaken) while his spells are Maintained he has to roll Spellcasting vs. the Damage and exceed it or he loses BOTH spells. If Shaken from a non-damage source (Tricks anyone?) then he still has to make Smarts Check (and I suspect he has not put much into this if he is more warrior based than spellcaster based). Keep in mind on the damaged version that he is at -2* since the penalty for any Maintained spells is for any arcane check (and minus and Wound Penalties he might have from the attack itself). If the PC is more Warrior build than Mage build, then they are going to run short of PPs. There are only so many fights they can get into with this tactic.
* (for those not familiar with Savage Worlds: -2 is a BIG penalty).
Quite frankly, he is just replicating a focused fighter-type with what you have describe. I think you institute this nerf you need to let him rebuild the PC, and I think you find he can replicate much of what he had without even using an arcane background - so it will be "active" 24/7 instead of just when he casts the spells.
As an aside, we did a full 0XP-100Xp campaign that had Psionist (my PC) and a "wizard" that eventually used Quickness and Bodyguard/Summon spells. My PC had neither, yet I felt my guy was as good overall as the other PC. His PC was really good at "taking out the trash" - lots of Extras would quickly disappear under the waves of creatures and Bolts. My PC was especially good at taking out Wild Cards - Telekinesis them out of the way, Puppet them, etc. After running and playing in Fantasy SW games have no problem with Quickness and Bodyguard/Summoning spells a GM or player. What I did see was that since this other player and I ran rather focused PCs we could really rip things up in combat but we did have other holes in the game - weaknesses (if you ever hit my guy - it was touch and go if he would survive - a glass cannon) and less effective with the non-combat portions. The cool thing is that we likely will go back to this game as some point and I look to short up Weaknesses and other players can build up strengths - there is always some other advance to take!
Now Elan -- that one might be overpowered...I am not completely convinced it is, but another GM in the group would love to ban it.
