Technomancers have struggled from the release of 5th edition due to a number of problems. In 4th edition, they had a few features that made them broken-- The way the matrix worked at the time meant that any device slaved to a technomancer's "bionode" was literally unhackable by anything other than a technomancer. So in 5th edition, they nerfed the hell out of them (despite the fact that the very changes they made to the matrix in general fixed all the problems with technomancers already!) resulting in an archetype that was incredibly resource-heavy in character creation, and couldn't fill the same role that deckers could (as the matrix was designed with deckers in mind, and TMs were added as a damn afterthought because they existed already).
To show what I mean when I say "resource heavy", think of the Priority System.
A decker needs a lot of money, high LOG, moderate INT, and a decent number of skills.
A technomancer needs less money, but can't dump money the way that a decker can dump MAG/RES because they still need gear like every runner does. But the TM does need to invest in MAG/RES as well.
A technomancer also needs more attributes. In addition to LOG for skills, a TM's mental attributes become their limits on the matrix. Attack and Sleaze are the most important and most often-used limits, so CHA and INT need to be high. WIL is firewall, your defense attribute, in addition to being one of the two attributes used to resist Fading, and thus can't be skimped on either. Not to mention, a TM will take a lot more Stun then a decker.
Skill-wise, the TM needs just as many skills as the decker, and then needs even more for Compiling, Registering, and/or Decompiling.
So this is all a much bigger investment and it's a lot harder to balance, but if they're just as good it's no big deal. But... The matrix was designed around deckers. Deckers have higher dice pools than TMs because they are able to use augmentation to boost their LOG (and have more attribute points to spare). As well, many cyberprograms a decker can get for the piddly cost of 250¥ are required to do basic matrix things like cause biofeedback damage. A TM cannot do those things unless they spend 13+ karma, which is an absolutely massive amount for such an incredibly cheap item. Then you consider that TMs cannot slave any devices to their Living Persona, and so can't protect their gear (or their team's gear) as well. Then you factor in that a TM takes Stun damage whenever they would take Matrix damage. This means not only do they fall unconscious instead of being bricked, but it means matrix combat will cause Wound Penalties (which doesn't happen through a cyberdeck) making them even worse at it. Finally, because a TM doesn't have the money and wants to avoid lowering their Essence, they can't use augmentation to help them fill non-matrix rolls, have no way to boost their Initiative outside of drugs, and are generally worthless in a fight. Unless you wanna spend even more of your precious skillpoints and little money on drones.
And this is all for... What? Complex Forms? They are all mediocre, and until errata, had hideously high Fading values that basically killed you if you wanted to accomplish anything with them. Sprites are likewise underwhelming, as their dice pools are often even lower than the TM's. A chargen decker will usually have 12 in most skills, and 14+ in the ones they use a lot. A F6 Sprite will have 12 in its skills and can usually only use 2 or 3 of them. They blow through Tasks quickly and so cannot be relied upon for most extended hacking, and the marks a Sprite gets are not shared with the TM, meaning they can't help you get into hosts or download files.
It sucks.
It's been years, and technomancers have gained almost nothing in the books that have come out. Data Trails promised to fix the issues with TMs, and instead offered about 4 pages of awful Complex Forms and even worse Echoes that hardly added anything worthwhile, let alone fix any of their existing problems. The book then continued to ravish deckers with new toys and mechanics, and an entirely new system that... Oh! It needs you to have a certain cyberprogram to do any of it! Meaning 250¥ for deckers, and 13+ karma for TMs.
Someone came on to the forums and said she was going to begin working on the supplemental book that TMs needed, to include fixes and all the material from 4th edition that was just never included in 5th edition (like the Technomancer-equivalent of Mentor Spirits). She made the first post, and then never posted again, and said almost nothing for years save for a twitter post about how she somehow misunderstood a coworker's joke so badly that she genuinely thought she'd been fired on the spot.