No, I am not saying that. I am saying that sometimes they are "optional", in the sense that anyone part of the magical tradition can carry out some activities, but characters with a related ability might add it as a bonus. For example, every folk witch knows how fix arcane connections, but only sahirs versed in Solomonic Astrology do. Every sahir knows how to initiate other sahirs in the Arts he knows, but if such a sahir is also good at Solomonic Travel, it's much easier - in this case Solomonic Travel is optional. Ideally, it should always be stated when supernatural abilities are optional and when they are not; the sahir mechanics do it, the folk witch mechanics do it for pretty much every activity except longevity rituals and familiars - that's why I asked for a clarification!
Not really, it depends. A Gifted, intelligent individual can help an Hermetic magus in the lab as soon as he has a score of 1 in MT, no need to open the Arts. An unGifted mundane who has undergone her first initiation as a folk witch, and has gained a score of 1 in MT may fix arcane connections (something a sahir needs Solomonic Astrology 1 to do) and perform any other folk witch activity without explicit requrirements, like analyzing potions.
No. To be a folk witch, you must have either your Gift opened, or you must have undergone at least one initiation. Now, suppose you have only learnt how to fly a broom, and your MT is 1. Can you bind a familiar? That's unclear, but assume the answer is yes, in principle. Ok, you need to match 10+its might+its size with Int+MT(1)+Aura. So, well, yeah, at this point you can maybe bind a non-magical cat (size -3) if you are pretty smart and in a reasonably strong magic Aura (Int+Aura at least 6)... and have already befriended the animal (with which you can't speak, so at the very minimum it will be pretty hard to get him learn MT - no help in the kitchen from it). Sooo... hmm... now you have a True Friend cat with Int-3, but somehow I fail to see how you've broken the game.
What if we say such a young apprentice can theoretically create a longevity ritual for herself? Well ... if she's 10, she might pull it off (she can use 2 pawns of vis with her MT 1), and gain a bonus of 1, possibly 2 (int+Aura equal to at least 5) to her subsequent aging rolls until she fails one. Of course, if she's 11 or older, she can't pull it off, as she'll need 3 pawns. Again, it does not quite feel world-breaking, or inappropriate from a flavour point of view.
It may be ridiculous, but it's canonical. Because that part of Solomonic Travel has been integrated in the broader framework of the sahirs, unGifted Solomonic Alchemist can initiate others in Solomonic Alchemy, using a method that benefits from, but does not requrie, Solomonic Travel. Similarly, inventing naranjs benefits from Solomonic Astrology, but explicitly does not require it.
No, see above. Though I do agree that situations in which a supernatural ability benefits, but is not required in, a magical activity are uncommon.