So here is where you're off base. 1. No one in tier 1 is going through 4 combats in a day, let alone before a short rest. The party would die. There aren't enough resources.
My notes from running Sunless Citadel most recently: PCs fought wilderness blights rats, rat, 2 mephitis, (met) Meepo, and a rat swarm - and then took their first short rest. They then met the Kobold King, and were afforded the chance to long rest. There was also some traps in there. They advanced to 2nd level at that time. This was atypical as I find - even though level 1 is very short if you follow guidelines - PCs usually rest once or twice before advancing. They then proceeded to fight through the goblins and enter the lower level. They took 1 short rest and one long rest before advancing to third level early in the lower level - after 13 more encounters. They finished the adventure *without resting* and then started Forge of Fury as 3rd level PCs fully rested and close to 4th level. Their first rest was a Long Rest after the Orc Shaman.
I don't feel like that experience was atypical.
2. If the druid is tanking, he's probably not going to come out of wild shape just to cast 1 spell, that just sounds dumb.
But they'll leave it so he can be a halfing to get slightly better initiative for the next combat? And forget the dying fighter - he doesn't need healing because I'm a BEAR!
3. Small combats, he may not decide to wild shape. There are plenty of combats that I don't. I've even played whole adventures when I decided just to be a caster.
Yes - you do spend time outside Wildshape. You generally go for wildshape for the big combats, but you can't always tell when you need to use the resource.
4. If he does decide to come out of wild shape to cast spells, well, he's a caster, he will have plenty of spell slots at higher level.
And those become the focus of the character at higher levels, usually. Moon druids become the tertiary melee force and spend more time casting those more powerful spells.
5. Who cares what you've read what the optimal shapes are, I think I've turned into a polar bear once. Most druids transform to fit the situation.
Again, that is not what most threads from druid players indicate. They spend a LOT of time as bears. Not all druids, and certainly not the ones that are more highly RP focused, but most of the ones interested in fight strength do it. Honestly, not recognizing this makes me doubt how much you have played a druid.
6. How do they have weak concentration? Usually their animal forms have pretty good Con.
But are not proficient in Con. +3 or +4 con saves fail over a quarter of the time on concentration saves.
Also, they can take the war caster feat to give themselves advantage.
That is an option. Few druids have it before 4, and most do not get it before 12. Some never get it.
7. Wild shape lasts in hours equal to half your level, so you can, short rest and overlap shapes. You say you've played a druid to 13th lvl, but you sound like you've read how to play a druid off a forum.
That is what your post sounds like to me.
You don't sound credible at all. So I'll leave it at that.
I hope you do.
Regarding the elemental form - It is nice, but as you only get one use per rest, it can leave you formless if you have a prolonged adventuring day.
Different tables are run differently, but after level 4, the great weapon fighters tend to leave the druid behind as a melee combatant, and the spellcasting is hard to use the longer you spend in a form.