If they are not calling it Ignem, you are not playing ArM.
It adds incredible flavour, and that flavour is worth the cost of using the jargon, in my opinion. I think you are seriously misjudging the capacity of random punters if you think that is a barrier. Roleplayers are prepared to learn all sorts of mad terminology.
And they don't need to necessarially "learn" the terminology. Just start the game, possibly provide a short cheat sheet for terms like Certamen and Quaesitor (if needed in your scenario), and write a translation direct on the character sheet...Creo (Create) 7, Intellego (Know) 5, etc. Looking at your simplified version again, I would also recommend keeping the normal Range, Duration, Target jargon.
For me, the big barriers, are realising what you can do with Spontaneous Magic (and calculating through the level on the fly), and realising that the game is about magi. The other big barrier, for Con games, is that the full game is really about long-term play; the game is more about why the player characters are going into the dungeon rather than the actual clearing of "monsters" from the dungeon. This is difficult to realise in a con situation.
I like your idea of a menu for Spontaneous magic, but your list somehow loses something of the fiddly joy of calculating out "proper" Spontaneous magic. Although, I'm not sure what a better solution would be.
The clever thing about the ArM magic system (which the use of Latin terms adds to) is that when as players we use the system it feels a little bit analogous to the esoteric calculations that the characters might be doing. You use the jargon and do the calculations because it feels "in-character". Which is fantastic.
Basically, you seem to be stripping out the bits that make ArM interesting and different. Which, if that's what you think you need to do to make the game accessible, is hardly a good advertisment. The Arts and the magic system are the good bits about ArM, in my opinion. They are what you should be advertising, and emphasising, not disguising.