Side facing radars and such feature on Russian fighters due to their general doctrine of unit self-reliance.
It was seriously considered (along with IRST, BTW) for the F-22, to the point that the production airframes were actually built with compartments reserved for the side-looking arrays. Were these omissions (to which you might further add the missing HMD) really due to lack of need or rather a lack of budget? I would hesitate to jump to a conclusion.
Western doctrines make such features pointless with the superiority in numbers, sensors, AWACs etc they have.
It is worth noting that the USSR was (along with Sweden) was one of the fastest adopters of intra- and inter-flight data-linking. By the early 1990s, there were about 1000 Su-27s and MiG-31s with such capabilities in service, against <100 F-15s and F-14 with JTIDS in the US (the fact that Link-16 is more capable notwithstanding). It took the US the better part of a decade to reverse that situation with the lower-cost MIDS terminal.
This is one of the most common misconceptions about late Cold War Russian fighters, and the reason why the popular dismissal of the Su-27's combat effectiveness based on extrapolating its similarity to the MiG-29 in terms of avionics is so incorrect. Yes, the radar is based on the same technology (apart from being larger and hence longer-ranged), but the Su-27 has the TKS-27 intra-flight data-link which completely mitigates the poor situational awareness so often criticized in the MiG.
Quite apart from the fact that *early* Teen-Fighter radars were nowhere near as good as people frequently assume based on the specs achieved in later models (compare the number of targets tracked or the MTBFs to the N001 and the latter doesn't look so shabby at all).
Weapons bay configuration seems like a weakness to me. Small capacity (pretty much proven), bad layout (centre of mass changes more significantly than the conventional layout used by F-22) so really not any better than its peers.
Small weapons bay capacity? Show me another fighter that can hold 2 SRAAMs + 4 (!) 800kg JSM equivalents internally... Certainly not even the F-35, and in terms of A/G munitions that's obviously one of the best 5th generation contenders.
The modest (MR)AAM load on the Su-57 is weird but certainly not caused by lack of bay volume. Even allowing for the problem that the precise dimensions are not known, it's almost a certainty that with folding tails on a R-77-like MRAAM (minor mod, they already fold for ground storage) each main bay could hold 3 missiles.
As for the CoG changes due to the tandem bay configuration, Sukhoi is intimately familiar with a very F-22-like layout from the Su-47 and considered it again in one of the designs leading up to the Su-57. If it was superior, why did they abandon it?
We've never seen a genuine photo showing capacity or firing. Why assume Su-57's weapons bay is something to be "liked" as they say.
Until 10 November 1988, the public had not seen a photo of the F-117 either, yet it had been in existence for 7.5 years by then (and considering its combat debut came just over 12 months later, it will have been dropping bombs before then). Just because there's no photo doesn't mean it didn't happen - we've not seen a picture of the bay open in flight to date either, but thanks to a leaked slide it is known to have been done by 2014 (quite apart from the mock-up bay flown on the Su-47 in 2008).
SU57 is not a Short take off bird in the same way. It needs some length to get airborne but the Russian concept pushed for less care as to the overall state of the field.
In fact I think they're overdoing it in that regard. Looking at the relative location of the nose wheel(s) and intake apertures on the F/A-18 & YF-23 suggests the Su-57 (and perhaps Su-27 family) might actually get away without FOD screens in the intakes according to Western practise. Given the weight and maintenance burden, that has to be a tempting consideration.
