I haven't tested howitzers enough to see if they work better or not, but the new SP-only objects have identical raised perspective to the ones in the 2.25 minimod - they're just new objects/entities that only appear in SP and co-op maps.
I have, however, already coded howitzers to fire HE only, in the hope this might make them more effective. One reason they don't work properly may be that bots treat them as direct-fire weapons (as their primary shell type is AP, direct fire); disabling the AP shells might fix this.
The problem, though, may be less to do with any hard-coded difference between howitzers and mortars, than the fact that howitzers are usually placed a long way from the front line (and often behind visual obstructions like treelines and buildings) so rarely get the chance to see enemy targets, even with the raised view perspective.
Nebelwerfers seem to be usually placed closer to areas where combat takes place, so get more of a chance to fire at things. They're the only non-mortar artillery I've regularly seen firing at anything, though the 25pdr on Supercharge will occasionally fire AP at German vehicles that get too near the British main base.
I'm planning to try setting 20mm-equipped armoured cars to IsAntiAircraft=1 (currently it's set to 2, for opportunity shots only), if it doesn't distract them from ground targets too much I'll keep this change in.
HE shells (for all weapons) have the same maximum range as AP - 500m - and I've noticed tanks are much more effective with HE since my last update (with the new armour classification system) though they're still not perfect.
No idea about the fleeing/evasion code, I might look at this later though, I suspect it's in the AI behaviour file, possibly increasing the "take cover" priority will help. I think it's also affected by the "explosion radius" setting for weapons - I deliberately disabled this for AT charges, as their throw range is less than their blast radius so bots never used them - I thought kamikaze bots would be preferable to ones that never used explosives at all
Haven't seen tanks fire smoke rounds yet, infantry will still (sometimes) throw smoke grenades at vehicles and guns, but won't drop them randomly anymore (this was caused by the same C4 code that caused the satchel TKing)
Tanks should, theoretically, use special AP rounds against heavy armour, but don't always do, maybe there isn't enough difference between the AP and special AP target priorities.
The AI's reluctance to use the guns on Kidney Ridge may be partly because a lot of them are miles from the CP's spawn point; even the Pak38s are rarely occupied. The mortar and flak gun inside the base itself almost invariably get used.