All the same, just a notch faster, that sums up what the 3400G really is. Aside from a frequency bump on the CPU cores and IGP, we're really looking at a binned 2400G here. So while I can understand as to why AMD wanted to position this APU in the Ryzen 3000 range, it really does not belong there as you do not benefit from the architectural improvements ZEN2 offers, as well as it's increased IPC. Make no mistake though, for an APU it is a spicy one with a strong graphics engine and very decent clock frequencies on the CPU cores. At a selling price of 149 USD, the Ryzen 5 3400G might be a notch pricey compared to the 3200G through that one is 50 bucks cheaper. But the 3400G does offer you SMT (hyper-threading), which does help in offering you a bit more bite on generic processor application performance.
AMD is offering merely an incremental performance increase with the Ryzen 5 3400G. As an APU these units still hold ground, but as a gaming processor, these obviously are not rather exciting processors. I think it is confusing for the novice buyer that is pursuing a Ryzen Gen3 product, to spot a Ryzen 5 3400G in the stores based on Gen2 fabrication,. These APUs are not fitted with ZEN2 cores so they lack the architectural improvements and increases in overall IPC that ZEN2 offers. So this remains to be a Series 2000 APU based on ZEN+, plain and simple. Regardless of what you think of all that, it still is a capable CPU with an IGP that Intel has issues keeping up with. However, and this has to be said, Ryzen 3200G/3400G biggest competition is not at all intel, it's the Ryzen 2200G and 2400G.
Slightly tweaked these procs offer the same performance at a far lesser price as over time the prices for the 2200G for example now is 79 EUR/USD and that 2400G 119 EUR/USD. And if you don't care about that integrated GPU, may I remind you that a Ryzen 5 2600 with six cores can be picked up for ~125 EUR/USD. That is a proper processor and will flat out beat CPU performance on all levels incl gaming (with a dedicated GPU) compared to these APUs. So yes, I have somewhat mixed feelings about the 3400G and it's current positioning. Only if you need a solution with IGP it would make sense, but even then I'd steer you to the cheaper but near same 2200G/2400G. Once prices come down they'll probably start to make a bit more sense, but currently, we fail to see its relevance for the market.