And quite maybe Edelgard's subsequent opening moves, but I'm less on about that. I'm also specifically talking about the Empire-Alliance Stalemate, rather than the Empire-Kingdom/Church one, but I mucked up the title.

CF was my first playthrough and I've been replaying it again recently so this has been on my mind. While the exact state of affairs is kinda believable, the explanation that we get via dialogue for why the stalemate exists between the Alliance and the Empire is... weak, at best. While not opening another front with the combined Church/Kingdom army kicking Imperial ass the past five years makes a lot of strategic sense, the way the Alliances' position and Edelgard's refusal to attack it with a clean sweep is poorly explained in game; Claude is trying to maintain neutrality while... making the alliance look discordant and divided? Edelgard doesn't seem much for needing another Casus belli so if the Alliance was giving off a position of weakness, that'd be the perfect time to attack, consolidate the conquest and open a second front against the Kingdom that bypasses Arianrhod. Yet we're supposed to believe that Claude's 4D chess that feigns weakness, rather than presents strength is what keeps Edelgard at bay.

I think this is egregious because there's a better inuniverse justification that could be used, and syncs with the aforementioned state of the unfinished war in the north; Almyra.

The Alliance, particularly House Goneril and Holst, is the bulwark for Fodlan against invasion from Almyra. The neighbours to the east have attacked before, and while beaten back are still a plausible threat. It doesn't take much more than a dialogue change to our good Spymaster Hubert explaining that over the past few years, Almyran clans have been putting their conflicts aside and possible assembling a large army; both the Imperial intelligence and the Alliance suspect an invasion is possible, especially if the war makes Fodlan look ripe for the taking. If Edelgard opens an invasion against the Alliance, her army temporarily cuts Fodlan's locket and the Alliances best general off from reinforcements and supplys and will potentially win a Phyrric victory, leaving itself weakened and prone to the Almyrans invading and reeking havoc. As such the Empire has put off a campaign against Leicester and left them be for now.

This together with Claude trying to manage pro-imperial vs anti-imperial factions makes a way more plausible explanation for the stand off state at the beginning. Even using that they need to maintain defense of Fodlan's locket could be a means for Claude to keep the likes of pro-Imperial Gloucester in line; fuck Edelgard's War, "we're sitting this out and watching the flank of Fodlan for the time being, we'll deal with the aftermath."

Of course this actually sets up for an even better surprise, while still forshadowing fighting Almyrans, when Claude reveal's he's called them in as allies. If Edelgard still goes for the clean sweep against the Alliance move upon your return, which is justifiable given Byleth is a trump card, what could be expected is crushing Claude and then consolidating the defenses of Fodlan's Locket before the Almyran's invade/besiege it; only to be surprised when they're let right on past and the past several years have been Claude building an New Alliance. Better characterization for the schemer side of Claude all around.

I think the opening stages of the war with your return could also, and I'm slightly inclined towards, being pushing the offensive against the Kingdom only for Claude to surprise you with Almyran support. I'd still prefer either of these over the current set up though.