Resident Evil 5 mercs scoring design is a great fit for the rng heavy, beat 'em up style game it is.
The scoring basically has 3 layers - combo chain, killing all enemies and time bonus. The 3 layers are really well synced to what I think players care about as they get into ANY scoring system.
The first and most obvious layer is kill combos - this is the first thing players will notice, it's hard capped, its exponential-ish (50+ combo adds 1000 puntos per enemy kill) and it's all-or-nothing - if you let the combo drop you get nothing. All the benefits of a Dodonpachi style chaining system are here. This gives the player a very immediate, clear goal with extreme punishments & extreme rewards. They know exactly what to do, what the success state is, and what the failure state is. Keeping the combo up is fairly challenging but not too tight - if it was the only scoring mechanic and was tighter, the game's copius amount of RNG would screw over the player a lot. You know when you get so good at a game that the enemy behavior RNG doesn't matter cause you can easily react & deal with all of it? The leniency allows for this, you can "outpace the impact of the RNG".
The second layer is the enemy limit. The levels will only spawn 150 enemies and some midbosses, if you kill them all you finish the stage. This flows smoothly between the combo (more enemies = higher combo and more ways to cash in on your high combo) and the time-based scoring (you gotta kill stuff quickly otherwise you won't have enough time to spawn all 150 enemies). This is a bridge between the 2 scoring mechanics of the game - the player's learning how to factor in time. Once again, it has a very clear goal with a hard cap, and some smaller sub goals which is killing the bosses which give you more puntos.
The last and most important layer is the time bonus. Every time you kill an enemy with melee attacks or break a time bonus item, extra time gets added to your counter. Once you reach the 150 enemy kill limit, all your leftover time gets converted into points. This is the final, granular and uncapped layer to the scoring system. Clarity disappears and all the enemy behaviors start mattering, including all the RNG. Where enemies are, how many of them there are, what they're doing, where you are, which weapons/items you have, etc. all affects the scoring and the optimal solutions to any situation become extremely hard to figure out, while RNG constantly forces VERY suboptimal situations on you. This layer is the most linear, there no multipliers or bonus chains, it tries to average out the RNG as much as it can. By the time the players reach this point, if they reach it, they will probably enjoy putting up with the game's RNG.
So :
- Top Layer (most obvious to new players) - all-or-nothing, exponential, hard capped with a low skill ceiling
- Middle Layer - transitionary layer
- Bottom Layer (the real meat of scoring, for high level players) - highly linear, granular and with no skill ceiling
It's a way to get the benefits of both linear and exponential systems while minimizing their flaws and minimizing the negative impacts of RNG.