Competitiveness balance

I get where you're coming from, but at the same time I can't really give any advice. I personally just play the game, going from tier 18-19 constantly because I don't have high enough merged units (Highest one is my E!Chrom, +3), but I still think the game is fun, even if I'm not in the highest tiers ^^;

I agree. I think arena needs a redesign from the ground up. In a game about building units it's frustrating when the supposed endgame mode is so restrictive. I hover between T18 and T19, and even then, it's surprising how little wiggle room I have for team building. The new update only made that worse.
There may still be some variety in defense teams in my Tiers, but it's still armors and dragons like 50% of the time. And Arena at it's highest is absolutely disgusting with it's Armor hell. You can't deny something is wrong when you see full armor teams with DC weapons AND A skills...
I say IS should start from scratch, removing BST and SP scoring altogether. Actually seeing variety in teams will make Arena less predictable, and thus harder.
I also think there should be a score bonus for winning match-ups quickly.
I hope what you are saying didn't go completely over my head.

I've been pondering this question myself, and I've actually semi decided to retreat from arena temporarily. I might drop down to tier 16 or something if people go hard on bonus unit kills and I don't; I'm not sure that I care. I need to slow down and figure out what I'm trying to do in this game now that the system has gone the way it has gone.

Just to get this out of the way, SP-based scoring looks like it's here to stay, as evidenced by Ostia's Counter being 350SP and death blow 4 being 300SP. I think that means BST-based scoring is also here to stay.

I'm starting to think of arena as its own game. It's not really Fire Emblem anymore. It's a really weird engineering contest to see how much BST and SP you can spam building support units to make your bonus unit kill everything. As I have expressed in other places, it violates a principle which I hold as eternal and essential to justice, which is that the strengths of a thing (in this case, a unit) are admired instead of just looking for ways to warp and distort it into the purpose of some fallen mortal's vanity. That's not a game I want to play. Play prepares us for activities with greater implications. I hear that serial killers and rapists are observed trying out their violence on dolls and animals before targeting human victims. The arena scoring system as we have it today is training us to abuse the creation we are to care for, both its animate and inanimate parts. I don't want to practice for that; my past is distorting enough and even if it wasn't I still wouldn't want to practice that.

It's become clear to me that building for that game is completely different than building for any other aspect of the game, including PvP modes such as GC or even arena assault. Arena assault still has the BST-and SP-spamming component, but that at least is half tolerable as a restriction that challenges the team-builder. If arena didn't require merges, I would consider playing. It would be like those GHB quests which specify things like "defeat Corrin using Sharena" except now you get screwed up stuff like "defeat Myrrh using Sharena." However, since arena scoring requires merges (when perhaps it should decrease score for merges, because it takes more skill to fight at a merge disadvantage), there's no way I'm focusing myself on this decidedly bad game. I'll make my favourite units succeed as well as they can according to the kinds of opponents they face in arena, but I said before that this game has taught me about investing in what I really care about, and I'm interpreting the latest change in arena as just a persecutory trial. The establishment has decided to punish good, sound play and the respect of units' strengths; it also punishes players for investing in units that have great potential as combatants rather than as mere support units when in fact balance and complementary roles are important to a team. I have decided. I will play the units I love most, and I will invest in them. Even if the system refuses to reward good play, I will pursue it, and even if they keep introducing worse things than bullsh** fighter, I will continue trying to make my units do what they do best. (I may also invest in additional units to deal with new threats, if that is what they do best.)

In any case, what do we want orbs and feathers for, but to spend them on our favourite units? The proverb says, "better is a handful of quietness than feasting with strife." It is not worth to be stressed, anxious, and upset trying to get a few orbs and feathers. I will accept a lesser income to remain true to who I am, my own style of play, and what it stands for. Am I not a musician by trade? I have perhaps greater need of such understandings than people with steadier income, the validity of whose occupations are not as often questioned (ex: medicine, engineering).

Don't sell out to a system, especially one as bad as arena scoring based on bonus unit kills. The riches and acclamation of mortal men and women are not to be compared with what is eternal, beautiful, and, it seems to me, peaceful, of which our play can be a microcosm - if we accept to let it be that rather than tribute to what is false and detestable.