As a Tahm main, if you want to make a change, I'll make you an offer.

I always thought his devour worked a little funny. The damage happens as a single tick that happens once you get spit out. I know this is because whoever is eaten is in stasis (save for ignite for some reason. The amount of teammates that just fell out of my ass is kind of funny). This caused a couple problems. 1. Initially, there was a brief moment where you could activate a shield before the damage ticked on the way out. This bug was fixed. (many consider this a buff for some GOD forsaken reason.) 2. Targets that are eaten have a .2 second moment of invulnerability before they're actually eaten. That has not been fixed.

All the sketti code aside, I think that damage should scale with how long targets are in his stomach. Really, just make it do half damage for a mid-swallow regurgitate and scale up to max damage at full charge. Bump the damage up 1% max hp at all levels and 2% at 5. Done and done. All the other mechanics of devour make sense. It makes sense that quick-blasting a minion does the same damage as storing it for a little while and the armored vehicle mode does no damage.