I don't think Leif is the only character in the series to make massive mistakes or is incapable to do certain things and be punished for it. This is a prime example of why I find Leif to be overrated - when talked about he is presented as a more flawed character than he actually is and other, actually good and interesting characters are thrown under the bus and ignored like as if they have no merit. I'd find Leif more tolerable if his fan base wasn't so keen in over glorifying him, which is amusing since the same fan base complains about Kris, Robin and Corrin being over glorified when honestly to me it sounds like Leif is glorified more than any of them and what infuriates me more is that he does not deserve it at all. He has less personality than Robin and Corrin, and I guess it works because it makes it easier to project to him and relate to him but it just does not cut it for me.
I cared about the events in Manster and about Eyvel but after the Manster arc I really started losing interest. Maybe if Leif actually had more characterization, and the people he interacted with had more characterization as well as had some form of interesting relationship with them, then I'd definitely care more and have it sink more in me. Even the mistakes he did too wouldn't fall so flat on me because I'd actually be given a reason to care. All of his screw ups feel meaningless to me because I don't care about anything bad that happens because of his mistakes.
The fact the game rewards you with very little is not a positive aspect about it. It just makes it more of a slog overall and even more meaningless than it already is. It's fine to have smaller scale war and conflicts but that doesn't mean it excuses them from actually being interesting. Just because there's less doesn't necessarily mean it's better. I found Leif to be a good enough combat unit with good investment and he does have good utility so saying he's weak falls flat on me. The two tacticians characters are also incredibly boring characters and I had finished Binding Blade just a few months before starting Thracia 776 which already had the awfully boring Merlinus for Roy. The death of one of them fell flat on me but I vaguely remember one of them having some bite to them in criticizing somebody once. They were like Lewyn in Genealogy, but there were two of them for a while. Leif's maturity literally flew over me because he lacked so much characterization it didn't fell like it happened. Anyway, Leif screwing up as much as he did was mostly because him being in a Gaiden means that since nothing matters that much, him doing things that don't end up mattering is fine. The other characters don't have that privilege but what the writing team for Thracia 776 forgot about is actually giving weight to the shit that was happening. I CARED about what was happening in Manster because Eyvel got captured and was lost to Leif. Eyvel was a mentor figure to Leif and they had an interesting relationship that didn't seem like it was work related only, so there was actually weight to what was happening. This could have served as some really good plot for Thracia 776, to save and make up for your mistake in a war, to see Leif's drive in wanting to save Eyvel and how it makes him change and develop as a result. Instead, Eyvel's existence and being saved is ignored or not treated as something important until you are able to save her in a gaiden chapter. Suuure, maybe I put too much faith in Thracia 776's plot, but I wouldn't be complaining about Eyvel motivating Leif a lot being a good plot if the current plot was good.
The map design started getting more annoying than enjoyable and weirdly enough the fan base considers the Manster chapters hard when I found them to actually be okay. While I understand that it needs an understanding of its mechanics to beat, there's a lot of vagueness and the fact that Kaga even admitted that he designed the game in a way to sell strategy books just goes to show how awful it is. I understand wanting to try to get as much money you can considering how late the game came out in the SNES's life but it's still awful.