man i played the game non stop for the whole weekend, currently at stage 39, the early stages are particularly difficult if played on hard, but the SRs aren't hard to get.
However, after the initial stages you'll start getting objectives like getting a boss under certain % of HP for it to retreat, the hard part is when you need to setup your supports and twins to kill them (instead of wounding them) in one move, this way you can get more experience and maybe extra optional parts by killing them.
This is not hard once you get Daizengar & Aussenseitter or SRX & R-GUN, but before that it takes considerable amount of effort to do 25k damage without them.
Now my boss killing setup is something like this
Initiate Team:
DaiZengar & Irm/Roa/Hugo/anyone with the twin spirit command that guarantees critical hit
Support Team:
R-Gun (Mai) & Seolla/Excellen, make sure your supporters have purchase the skill that removes support damage penalty (makes support damage 100%).
You'll wonder why i don't include SRX into the teams that's because SRX's tenjou tenja muteki ken has a armor debuff effect, which is excellent for dealing with bosses that has guard & potential activated.
There are times that you won't be able to debuff the boss, if thats the case then include SRX into your support team or initiate, Ryusei's twin spirit command also lets you guarantee a critical hit.
the key winning factor here is the critical hit command, i found it make a world of difference for dealing enough damage.
also, i still haven't seen hotblood or soul yet lol.