Let's talk about what you gain first. I don't recall the exact details, but you gain, roughly 30% damage reduction and 20-30% power damage boost (can't remember the details).
What did it cost?
- Skill points for starters. Skill points that could go into high-end ranks of incinerate, overload, or sabotage. But you also could have put the points into drone, turret, cryoblast, etc. Rank 5 (which gives the power boost), costs 15 points. An import only has 40 points or so.
- Skill recharge. 50-60% recharge penalty!!! That really hurts. Sure you can compensate by wearing inferno armor or something, but at what other cost? For every bonus you get on an armor set, there is the opportunity cost of other armor that you miss out on.
- Weapon selection. By relying on a power for survival like this, you hurt your recharge rate. So maybe you compensate by choosing lighter weapons. That can diminish gameplay if you dislike pistols or weeny SMG pew pew pew. Not saying I have anything against them, just pointing out what you may have to give up.
Sure dropping 15 points into a high level character is a moot point, but most Bioware games become silly easy at high levels. Weapon weights matter less when you can fully upgrade them, and use high level light weight mods. But when you start out, ... I dunno, it just isn't working for me.
1. I usually leave 1 point in Fortification/Barrier/Defense Matrix until I max my other more-required powers first. So for the Engineer, I max the three powers first (say Sabotage, Incinerate, and Overload), then Tech Mastery for more power damage. Then I can spend points into Fitness and the bonus power. I would probably drop a few points into Fitness to rank 2 to get a little more health, then spend on Fortification/Barrier/Defense Matrix.
My reasoning: the powers are more important than the passives since I want damage and debuff (or distract or whatever) first, then I can concentrate on increasing my power damage, then I can focus on survivability (health, shields, and damage reduction). I can live with 500 health and 500 shields for a while.
As for importing: importing a level 30 character from ME2 will give you 60 points to spend; this becomes 66 or 64 points when you reach level 31 when you land on Mars. This is enough to max three talent trees at the start of Mars. Most of my imports are level 30, so at the beginning of Mars I have my three main powers already maxed and I can begin spending points on my passive talents.
If you are importing sub-30 Shepards, then you certainly have fewer points to work with and have to make decisions accordingly. Understandable.
2. The penalty is not as much as you think. At +200% weapon weight, as -50% to -60% cooldown reduction it is only about a 0.5 second difference in cooldown, which is not that noticeable in-game. (equivalent to a +140 to +150% weapon weight). It can be important if you want to combo with your tech powers and want to carry a slightly heavier weapon.
In that case, you can leave it deactivated until you have enough points to max it all at once, or choose a different bonus power like AP Ammo.
3. Depends on the weapon(s) you want to use. With Sabotage, Incinerate, and Overload (and say 1-point drone for Guardians), you do not need to fire a shot so you can hold on to the Predator or Shuriken for a long time. If you really like shooting and you like using some heavier weapons, then sure, it can be a problem.
You sure cannot detonate your own combos if you use the Claymore, but if I want to use the Claymore I am speccing the Engineer differently.
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But again, if you prefer another Engineer setup with the Combat Drone, then go right ahead. I am not telling you how to play Engineer. Feel free to experiment with what works for you.
Use the Med Bay respec option to try different builds (don't forget to save your game first). See what you like or do not like. Maybe you hate the Engineer no matter what you try. That is fine; no one said you have to like every class.