@glossy relic SS can bite they are just bad at it yes so they don't because they have the advantage in the air. IR like to bite but cant because SS kill them too fast and they cannot stop it by any means, they need FS to be viable which is not productive to playing them.
IR v FS is good game play
IR in a 1v1 bite fight with FS is a 50/50 fight because FS has a lot of pierce armor and IR does not.
IR is close range with its flame so it cannot fight SS and its ability to flame FS is limited due to speed/turning, it requires skill and is good for the game
FS v SS is good game play
FS can fight SS if they can catch it which requires SS turning within FS damage area but because FS can tank shots and have fair flame range possible to win a fight
ASD v all is good game play
If the ASD gets the jump on FS or SS and you are not near water it has the advantage and can play around your slow hp/stamina decay
ASD can fight IR even with them having flame cloak because IR is so short range that they are not a threat unless you choose to enter their range.
IR v SS is bad game play
If the IR lands on the SS because they are AFK they can win as with FS/ASD
If they fight and are both aware of each other the
IR does not have the speed to catch the SS
IR does not have the range to hurt them in an air turn battle like the FS
IR does not have the stamina to stay in the air with them during the battle
IR does not have the sky box to stay with them during the battle
and to top it off SS does more damage than IR in their 1v1
the above listed items are in equal skill situation
Yes some of this is determined by players skill, a bad SS player will fly into an IRs mouth and get hurt usually not die due to fly speed and desync but take some damage.
In a 5v5 team fight you would want 2-3 FS and 2-3 SS with 1 ASD somewhere, the IR would not participate in a raid because it just dies to SS too fast. They are only used if it is your only dragon