I see what you mean, Zephira, that may apply to "some" things but not all. You see, Geyser may be a complex spell but not as complex and powerful as Dark Matter. If Lavos indeed took away his abilities to perform those spells, and Magus was able to re-adapt his mastery of Dark Matter, then why not Geyser? And instead of Magical elemental barriers, he uses Magic Wall?
Let me explain the reasoning behind the Elemental Barriers he uses against Lavos/Crono in 600AD. Not many kids would wanna see "science" behind a video game thus I last posted about... yeah... in one of the forums that's uninteresting to children below 13, but I'll try to keep at as basic as possible here.
Ever heard of the Enochian Sorcery? Or perhaps the Keys of Solomon? Ordinarily a summoning takes quite an amount of time and concentration to pull of correctly, and the entities of power that a sorcerer extracts beyond time and space is directly proportional to the sorcerer's ability. Even so, there's no guarantee if the entities, who have been summoned against their will, would submit to their summoners or attack them. In which case, two things essential things are needed.
1) Incenses - These may influence the kinds of entities that are summoned in various ways. Some may anger them, or some may subdue. The cleverest sorcerer would pre-plan and use them more like a sedative. Of course, this won't work against Lavos.
2) Pentacle - Contrast to what modern sorcery teaches, the circle is a form of order, and the center being the power. The most basic of pentacles hold elemental energy at certain points, but the most complex ones (if drawn properly) will give the sorcerer as much control over the elements within the circle. The reason for this is simple - protection. The sorcerer channels the elements of earth, water, wind and fire and surrounds himself within the barrier when he focuses the void beyond it, splitting light completely.
I mean think of it this way. You have seen Ozzie prepare a legion of zombies and demons, most notably Zombor which steals its victims bodies after killing them. Those demons actually resemble the "Ghuls" category of the Djinni/Dream Demons. Now, if Janus was to combine the Zealian Forms and Mystic Dark Arts, what would it lead him to? Lavos, of course! But just for that he needs to "survive that darkness". There have been many powerful entities he may have faced just to be strong enough to challenge Lavos's wrath.