The Tendi thing is basically the same move SNW made with La'an. It'll be resolved in the s5 premiere.

I did wonder why so many LJGs were on the bridge and why Boims got the chair, but I just chalked it to the usual - the otter more senior staff were up to something more important we didn't need to know about. Though it's certainly not unprecedented to give promising young officers the chair even when more senior officers are available. I take that as just part of Starfleet's training protocols.