Well, I'm surprised by your negative conclusions:
- I don't think that is really that slower than any other skillshot. And even though non-champ units can block it, they can be also used to guarantee a hit on enemy residing way too close to them (avoiding an explosion is a bit harder than the original blaze). So it's a double edged sword. I never had a feeling that the ability was too short-ranged or too slow, to the contrary. Especially on ARAM she's a great champ cuz of this ability (and of obviously too).
- Benefits of are usually fair enough for all-ins. This is imo the ability that corresponds to "E-sort" of spell in a generic champ kit: the last non-ult one that a player spares for special occasions like all-ins or escapes. I don't use or it often, but when I do and do it well, it gives a punch. It also synergizes pretty well with bidirectionally; a makes much easier and gives time for CD refresh and a 2nd easy-to-land .
- I'll repeat myself but I value a lot cuz of that MS boost. As for me, it adds to the value of flat shielding with proper use. Avoiding a skillshot is virtually almost equivalent to soaking it up entirely with a shield. Not to mention if the reposition helped to avoid a dangerous trap/gank. What's even more, MS can be used also offensively much better than a flat shield. I personally rate her among my most favourite ones.
To be honest, I like her current kit design a lot. I find her to be flexible and quite all-rounded, while still able to swiftly specialize to needs. Her versatility imo allows for so many very different build paths. Very often when I'm just not sure what to pick, she's my safe option. Of course I still lose often, but at least she gives me that kind of safe feeling of potential and possibilities at the start. Therefore my loss was well-deserved for our further in-game actions.
However, I must agree that according to GG, her winrate is kinda lower. Hence maybe it's really only my personal taste that I enjoy playing with her so much.