I guess it depends. I feel like mission/fleets depending, the cards will be stacked against you. Other times it will feel like it's faceroll levels of easy.
Convoy is one of my least favorite missions so far, especially if you are defending against Eldar or something. The in-game "hints" say something about spreading your convoy ships out, but I'm not sold on doing that yet. If you're defending against Chaos or Eldar, they either have good speed or range and I feel like you'll end up spreading yourself too thin trying to defend a line of slow-ass convoy ships while they'll start picking convoy ships off. I've had better luck clumping them down one of the sides of the map and running my entire fleet next to them, and just Alpha-striking the closest enemies that get to you first. If it looks like the rest of their ships will make it to you before you can wreck the first ones, I'll just drop a wall of stasis bombs to give me time to finish off the first 2-3 ships. Normally I just toggle Brace on a specific convoy ship when they start getting shot, repair when they start losing armor and AAF at every opportunity, more or less.
Assassination is another one that I don't particularly like. I think you get 3 minutes to pop the opponents Admiral ship (or defend your own). Depending on the two fleets involved, 3 minutes may not be a remotely realistic amount of time to get there and pop a ship, and past 3 minutes you have to use boarding actions and lightning strikes (teleport assaults) to try canceling the target ships attempt to warp out. You can totally get screwed by RNG here, especially if the ship (normally being the largest) has a high troop %. I've had to use every boarding action and lightning strike my fleet had to stop a target from warping away a number of times, at which point, if you can't wreck the ship before their warp refreshes (it has a quick refresh, quicker than your assaults do, by far) they'll just warp again and win. Then I have to start ramming them...
I've had Orks vs Eldar on Assasination...not a lot of fun when the Eldar capital ship can run rings around you, and I had one game where I finally managed to corral it in a corner...only for it to successfully warp out on like it's 3rd attempt or so, seconds before I could get back into range.
But anyways...if you're playing solo skirmish, I think that there are times when you see that you aren't going to win the mission via victory conditions, and I start thinking like"ok, I'll just try to pop as many ships as possible to farm Renown". Also, I've had times when things were looking bad and my choices were to either risk 'losing' ships for a shot at a clear victory ('destroyed' ships are just unavailable for the next 2 games until they repair on their own, or you spend Renown to repair them instantly), or to back off a little, brace my damaged ships or run them away (maybe even warp out) and try popping a few escorts or whatever I think I can still manage.
I'm not sure how other people feel, and I haven't looked up discussions about this online, but I seriously feel that at times Renown > Everything Else, including winning missions. I personally find myself focusing on destroying as many enemy ships as possible and trying to prevent enemies from warping out so you can get the Renown from destroying them completely, rather than worrying too much about victory conditions.