Alright, I said I was going to put DCS through its paces and that's EXACTLY what I did.
I started a fresh Prestige on Black Cat.
I did use:
200% Hero Synergy
10% Cyclops Synergy
9%, +1 Int Moleman Medallion (Level 25)
1 Int, 100XP per defeat Seer's Brilliance Uru Forged (Level 25)
10% Pot O' Gold Legendary
3 Int on a Pet Sentinel (I forgot to swap it with something else)
I did not use:
any boosts (cups, bars, iBoosts, Omega Boosts, etc.)
any XP Omega Nodes (no Int, no XP on kill, etc.)
any chests (Odin, Midtown, ICP, etc.)
any LQs (Red Terminals, Midtown, Hightown, etc.)
any special gear (XP on kill, min/maxed, etc.)
any Artifacts (no reason for this, I just forgot to equip them until after I was done)
I followed this path through the Story:
Shocker (including Flash-Bang Bridget and Thrill-Kill Karin, because I always kill them)
Doc Oc
Taskmaster
Hood
Safehouse
Elektra (including the named ninjas on the way up the tower)
Bullseye
Kingpin
Juggernaut
Magneto
SHIELD Science Station
Sinister
M.O.D.O.K. (including the Intelligencia quest)
Mandarin (including Madame Hydra and her Hulkbusters)
Heimdal
Kurse
Malekith
Loki
As much as I hate to say it...
Leveling feels MOSTLY fine as it currently is.
I was 59 after beating Malekith and Loki bounced me right to 60 for Chapter 10.
HOWEVER
That doesn't mean the system couldn't use some tweaking. The earlier levels flew past, leaving me over the expected levels for quite some time. This makes it feel that things like Shocker and Taskmaster are completely optional. Then later, I was struggling to stay close to where the next Chapter said I should be, making stuff like SHIELD Science Station, Intelligencia and Madame Hydra mandatory. Oh, and I totally skipped Doom, because...reasons.
If the XP could be smoothed out a little, it would end up feeling like hitting the supervillains is necessary, but the side-stuff is more "do it if you want to".
So, yes, I can admit it when I'm wrong. There is currently VERY LITTLE wrong with the DCS leveling system.
New players will have to work their way completely through the story (remember, I'm currently running more than 3X the XP that they will be).
People who love leveling can hit the highlights and take as much or as little time as they want (by using more/less of the options we have to speed up leveling).
People who hate "actually leveling" can spend money on boosts and skip the entire process as much as they want. :P