I find that alto needs less air on those bottom notes. I notice this especially when playing some Bach on tenor (the Mel Bay book by J. Michael Leonard), because I'll get to the end of a passage and haven't been able to grab a breath yet, and THEN those low notes need air support I have trouble supplying. But on alto or soprano, that's mostly a non-issue. I did have a bari for a while, though, and it did seem to play easier than tenor also, altho I didn't have the Bach book then as a comparison.Thing is, back in the 80s when I was probably playing and practicing 10 hours of tenor for every hour I played baritone or alto, baritone and alto were still easier to play.
Certainly small leaks will make the low register difficult. After overhauls on my alto and tenor, those bottom notes really popped out much so more easily, it was quite noticeable. Likewise, when the adjustment of the articulated G# goes even slightly off, it affects the bottom notes big time, because of the slight leakage at the G# pad.
Lastly, it's a matter of mouthpiece and reed. Or maybe firstly. Too large a facing can be a problem. I'm playing a .086" facing on tenor - pretty small compared to what's popular, these days but it's what I found works for me. And with a baffle insert, which helps getting more out of such a small facing. When I feel a reed is resistant on the low register (usually feels this way starting at the low D), I'll sand or scrape at the bottom 3rd or so of the vamp until it frees up and the low B and Bb are easier to subtone. I also use a Perfecta-reed gauge to take out side-to-side asymmetries. The difference is amazing, once a reed is symmetric and properly adjusted. I find that getting a reed just right can be a lengthy process. I use Hartmann reeds and completely re-profile them to the way they used to be (with an arched cross-section, not cut straight across).
One more thing, actually, and that is that the mouthpiece facing also needs to be symmetric. Even if you don't have a glass gauge, you can lay the mouthpiece against a glass slab and lay different feeler gauges between the mouthpiece and the glass - and they should lie straight across the mouthpiece, not tilting to one side or the other. An asymmetric mouthpiece facing will have the same effect as an asymmetric reed. Less responsive, more resistant.