The trouble is, nothing is explained in the game.
Especially not, that the available new stuff depends on the item YOU WEAR, and not what you have.
Than there is the problem that 90% normal you do with one rythm, than you hit the wall, and fer every new stages you have to buy a new weapon (and occasionally armor).
As there is no information available (ingame) I can not be '"misinformed". All my info is perfectly true though.
On shield: it helps absolutely nothing when I play. I either can kill everything, or everything passes me (for lacking enough damage), so shield is absolutely worthless.
Manaregeneration although is there, but the stages are simply not long enough to have it any use, outside boss-stages. The regeneration simply does not load back enough mana to cast a skill twice on a level. Well, technically of curse there is Granade, but that (and the other special attacks) simply does nothing to most, or at least the important enemies, So the only skill I use is Berserk, and you simply won't have 600 mana for a stage (maybe you can in extreme situation if you use it at the beginning, assuming you need it, but after the initial wave, so it is very unlikely, as you don't start with 100% mana).
And again: if you grab the equipment skills, you won't have the damage, what means you won't be able to kill the enemy,what means you won't pass the stages, what means you won't carry the items home, what means investing into equipment skills is not working. Unless difficulty 1 stages drop .the same as any other stages. Too bad I really never ever saw anything hero-related being higher than what I already have (I do gained regularly somewhat, like +100 dmg better ship-weapons).
The lvl 999 people I think abused a bug, or something. as someone yet to demonstrate how they got to that point (or they are actually payers).
So until I am disproved, I hold this is a pay-to-win situation, although by regularly adding people in 3s could likely help a lot, as I noticed the reward for adding people (again nowhere ingame, nor at the description is mentioned this) IS substantially higher than any other source avaiable
Of course I yet to try crafting, as I assumed it does the same quality-incrise like the shop. It definitely did when I tried it out at clvl 1. (I have ca. 300 gems, but the use of it totally depends on what the result can be from them).