Yes. I've had the same experience. I've had it go all the way past 100 damage. 90 or 100 is tagged as WARWHEEL and then after that it's like AXEL POWER or something. I definitely think the special was meant to be timer based and not damage based, since each consecutive hit deals more and more damage, and the different tags for the combos.
I've also experienced that shotgun glitch, which only happens with Axel.
RoadBoat feels like he has a similar one, but I think it may be intentional. After using his special, there's a long delay before I can fire any missiles.
Do you mean Axel cant use the shotty while in the Warwheel? That seems intentional, since he needs to use his arm to shoot, which he cannot do in special mode.
Interesting that you bring up Axel's combo feature. It definitely seems that the intention is time based.
I think that's great, but his base Warwheel needs to be altered, the main Axel complaint seems to be his warwheel is too easy to execute/is glitchy.
What does he start at, 70? He should start at 30, and every combo should add +15, so 30, 45, 60, 75, 90, 105, 120 tops, with say, 5-7 seconds to hit the combo chains. This should put his warwheel at 30-45 seconds. A good Axel player would make use of the Warwheel in cluster situations and would skillfully be able to strike up those combos.
His shockwave should receive a buff IMO and should be the primary special