While I would agree a far better solution for a fighter-bomber would be the Hurri-bomber or Beau, neither of these exist, and wont for some time. Even though a Hurribomber is possible in spring 1940, the need for fighters means it isn't happening until fighter production is acceptable.
The Battle isn't as slow or vulnerable as your suggesting; I think your looking at the OTL Battle - as has been written, Fairey offered a number of improvements to make it faster and more surviveable. It can also dive bomb if needed - it was designed to dive at 80 degrees, all it needed was dive brakes. Yes, it needs fighter escort, but its faster than a Stuka, for example.
It only needs three crew if you are trying to hit targets like Berlin, and you don't need all the kit added for night operations either.
Is it the perfect solution? No. But its what they have in early 1939.
Yes it is. ALL interwar medium bombers are and the fastest of them - the JU 88 suffers more losses than the Do17 and He111 . and the Luftwaffe loses around 36%of force in the battle of France against far weaker opposition than the RAF would face, This is acceptable because the plan is to win the war in a single campaign so high losses are acceptable. As is stripping the Flak units from Germany to provide a Flak Corps for each army group.
The problem being fighter performance is much higher whatever you do so if intercepted you are toast without a fighter escort. Strategically you might get away with it because there are so many targets and its not possible to maintain a standing patrol everywhere then its just maths, can the fighters travel from where they are to where you want them to be before the bomber can get there.
near the battlefield you are attacking the one place defending fighters will be in the air and over the potential target.
light flak will be deployed to cover any target the Germans regard as important. So essentially suicide unless you have a fighter escort. And if you have enough fighters to escort use them as the attacker if you need to do low level attacks.
Going to low level - which is inevitable in an accurate dive bombing attack puts you in range of light flak at your slowest as you pull out of a dive so the maximum top speed is not the metric, its the speed on pull out and vs the time it takes for the flak to train on target and shells to travel. Same with a low level, level attack, which is just not accurate. The Battle modifications considered are all about maintaining current performance by swapping out range or bombload for protection, which will make no difference in practice and the RAF knows it,
The BAFF instructions ( British Air Forces in France) note
Bomber aircraft have proved extremely useful
in support of an advancing army, especially against weak anti-aircraft resistance, but it is not clear that a bomber force used
against an advancing army well supported by all forms of anti-aircraft defence and a large force of fighter aircraft, will be economically effective.
The underlying problem is that the Battle is probably the worst in a class of useless aircraft once the single engine strategic bomber role is lost there is no point in building it. Of the total run of around 2,000, 500 are made after September 39, Once the RAF has the role of supporting an army on the continent its going to produce the aircraft needed for that role Ordering 500+ obsolete strategic bombers to do something you know they will fail at is pointless. September is the start of the war so fair enough. Pre war while you might look at converting existing aircraft and end up using them you realign production to meet projected needs, which now includes battlefield support as well as the ADGB and Strategic bombing. You can argue whether the factory space is best used for fighter or medium bomber production but the engine you are producing int he Merlin and if war is regarded a a material possibility well ADGB wants fighters and the Army wants fighters to keep the Luftwaffe off so build fighters. This is born out by the actual component of the Actual forces deployed.
The Air Component of the BEF is 5 sq Lysander, 4 sq Blenheim IV 4 Sq Hurricane to be reinforced by 4 Sq Hurricane on the start of hostilities. The AASF which has the battles is not part of the air support of the BEF, its there to bomb the Ruhr. With the Blenheims listed as Strategic recon not medium bomber in the Air Component.
Because one limitation is the skilled workforce. If you have them building light tanks, they aren't building proper ones.
The only reason for building a training tank in mild steel would be a shortage or armour plate, so that will only occur if that becomes a bottleneck. It didn't in OTL, so probably wont TTL
At least training the gunners is easier now
The other reason is so the tank can jump over canals. The serious reason is you can train maintenance procedures on a cheaper vehicle which you may get faster if you dont have to wait for armour so deployment to the troops is faster. Then it sometimes gets issued by mistake.
And you can jump over canals with it and ask for the 20mm flak rounds to be dug out of the armour because really fast and nippy and can jump canals and has served from Normandy - nd would continue to do so until they were reequipped with Comet.