The Evasion-system is supposed to (and to a certain extent, did) make light(er) mechs viable against heavier ones (heavier mech have usually more armor, harder hitting/more weapons), as (on average) lighter mechs can move further thus gaining more evasion charges (and their jumpjets cost less tonnage, so it’s kind of balanced with that too).
The Cover system is different, as we’re speaking about Mechs and not humans, LoS is a thing though, which makes it somewhat similar to PP. LoS is checked with “raycast”, and you suffer accuracy penalty for “indirect” fire (when you don’t have LoS but somewhat still “know” the target, either ally has LoS or “sensor locked”), but other than that shots can hit “not seen” parts too (if only the head is shown above a hill, you can still hit its legs with a laser… somehow), so it’s not THAT similar.
Cover simply provides 25% damage reduction, which is while not bad, a lot worse than “bracing” (ending your turn without shooting, 50% dmg reduction, can be activated after shooting if not moved yet with an easy to select skill, so trench-warfare is what most “lazy” ppl play).
This means that lighter mechs, who can’t trade hits with heavier, needs something to make them “more viable”, and the answer HBS gave us was Evasion based on movement.
You gain one Evasion charge for X movement and Y Jump distance, and every charge gives you a “passive” +Z% harder to hit to you. Any attack made against you will reduce your Evasion charges by one, but only once per attacking enemy mech, regardless if it was a “full salvo” or just a “lone” attack (the exception being melee attack with support weapons, which removes 2).
Now, as we’re speaking about mechs, the other system which works against Evasion is Stability. Once you become “Unstable” (received enough stability damage, from missiles/cannons/meele), you lose all Evasion charges. If you get enough Stability damage, you can get Knocked Down (though one salvo can’t knock you down, even if the stability-damage would be enough, there needs to be a second “push”), pilot receiving injury, enemy mechs can freely target any parts of your mech, like bodyparts in PP, which makes it important to guard against.
Bracing reduces Stability damage by 50% too, which means that Trench-warfare is possible against Evasion-warfare (which potentially negates everything, as enemy misses).
TL;DR: Evasion system is in Battletech to make lighter, faster mechs viable against hard-hitting, slow “behemots”, and while I find this a fun and tactical system (regardless of the balance-state in BT), I don’t think it’s needed in PP, at least not without thinking hard about how the Cover-system works. The easier it is to negate cover (like blowing it up), the more I see an Evasion-system useful.
I like it, it’s a fun single-player story-based game, but I was a backer, so I’m a bit biased
If you are not in a hurry, I would suggest waiting for a few more updates though, there are certain problems (like the “don’t waste my time” XCOM mod is needed), and without difficulty settings, your option for harder fights/campaigns are self-imposed restrictions, which while works, not ideal.
Mods will (and already do) help, but mods are mods, not everyone likes to use them