I have been running a saga since 2013 where one of the main characters is a Gifted sahira, and she filled the slot for a magi character.
Her player agrees with me that the character is underpowered when compared to the other magi, but not blatantly so. The worst part is actually the lack of spontaneous magic and the very low penetration scores, rather than the vis consumption. Though I must warn you that we're playing in the vis-rich Theban Tribunal, and that might have biased our views. Also, she's heavily specialized in Sihr (the summoning "Art"), thus she almost never needs to use vis at all when bargaining, and only does so to avoid gaining a bad reputation among djinn. This might also factor into our perception that sahirs are not such huge "vis burners".
As for their naranjs (spells) being mostly rituals, all of the solomonic formulaic spells can be cast as rituals. So, although most of the higher level guidelines require a spell to be a ritual, the vast majority of the lower level ones have "ritual" as a casting option, not a requirement when inventing the spell. The exception being Solomonic Alchemy, where rituals are all over the guidelines, and to a lesser extent Solomonic Travel. For the rest, rituals are the rule for higher level guidelines, but not so much for lower level ones, which neatly mimics the way Hermetic spells over level 50 have to be rituals. See The Cradle and the Crescent page 36 for an explanation of the ritual option for casting spells, and pages 49, 51, 53, 56 and 58 for the guidelines for each Solomonic Art.
My personal advice for you would be to boost Sihr, since that will allow the sahir to summon more powerful djinn and, most importantly, to bargain with them with ease. That will allow you to easily bargain them into a one-year service (see tCatC page 47 for the bargaining modifiers) that includes following him around and doing his bidding. This will make the summoning a yearly affair, which will greatly reduce vis consumption, and will provide the sahir with a djinni (or more than one) that will do his bidding, thus adding the djinni's powers to what the sahir "can do". Also, it will give him a big Summoning Strength, which will make casting spells ridiculously easy.
I will end up saying that fully stating all of the djinn the sahir summons is IMHO a must, so it would be best if the sahir stuck with only a couple of recurring djinn, best if enchanted as a khuddam (tCatC page 41).