Without the addition of planes to fill the gap, what is a better alternative?
Soldier on without.
Its not a good solution, but it's better than making really outlandish unrelated substitutes. For example, if we had a Blenheim that might be a better sub for the Heinkel, but the performance, speed, firepower, for the Betty is pretty darned different.
Sometimes there are subs that can be made that don't fully match, but look superficially the same. I dont think the Betty looks like the He-111. It could pass for some other things maybe.
The He111 is one of many glaring planeset holes. Ju88 probably matches it better, though.
Food for thought, in the last Rangoon discussion I made the suggestion of subbing the C.202 for the Ki-44 instead of the A6M5b. It has similar firepower, speed/climb, etc. It turns worse and is in-line, but otherwise is pretty close. Might consider a Ki-44 skin for that plane as well.