I never considered Dwindle actually. It's bad removal imo - the creature can still sit there and activate its abilities, e.g. it only partially removes Epicure of Blood or Dryad Greenseeker. It can also be removed in the future by cards like Reclamation Sage or Cleansing Nova. If my deck were short on interaction then it's a necessary evil, but as it is it's not a consideration.
I'm surprised modulo you don't consider Manalith an option. Ramp is ramp, and it can potentially enable a splash later (Rec Sage is a good card). Submerged Boneyard ... it's an on-color dual, but if I'm playing a 2-color deck I tend to prioritize these much lower. When do you run 18 lands?
Dwindle isn't THAT bad. You use it on a rather big creature (
Colossal Dreadmaw,
Frilled Sea Serpent) or an aggressive flier to lock it down. Some of these threats
Electrify and
Strangling Spores cannot deal with. It's a notably worse
Luminous Bonds, but Luminous Bonds is great and there's enough room for Dwindle to still be a solid or even good card.
Manalith is ramp and fixing, but not every deck wants to spend a card slot for that. Lategame, Manalith is much like an additional land without the benefits earlygame (for instance, you can keep some 2-landers, but you can never keep a 1-lander with Manalith; or some easy 3-land keeps suddenly become a lot sketchier if they are 2 lands plus a Manalith; on the flipside a hand with 5 lands and a Manalith is as much of a mulligan as a 6-land hand most of the time).
Manalith is a consideration if:
a) You're splashing (free source of your splash colour, which means you'll have to run less non-main-colour basics)
b) You need an artifact to enable synergies
or c) You have a LOT of top-end (8 or more 5+-drops) and not much curve beforehand.
Your deck fits none of these criteria and honestly, very few decks in M19 want Manalith (you rarely want to splash, artifact decks generally have better enablers, the high-end decks want different ramp cards like
Druid of the Cowl or
Gift of Paradise or are better off lowering the curve if possible)
An on-colour dual is better than Manalith because the opportunity cost of running it is much lower. Unlike Manalith,
Submerged Boneyard can be fully counted as a land at any time during the game, thus being run over a Basic. And while it may not seem like a huge improvement at first, a 10-8 or 9-9 manabase is quite a bit more reliable than a 10-7 or 9-8. You don't have to prioritize them highly, but they're good pickups if the other cards in the pack look like they don't make the deck much better.
I'd run 18 lands if I have good ways of using my mana even past the 7th and 8th land drop and/or I have a rather high curve but little carddraw/ramp. Since M19 has very few good manasinks, I'll rarely run 18 in M19; classic 18-land formats are Dominaria and Hour of Devastation.
Hired Blade was quite mediocre - it did work well with my other instants, but it didn't have much impact. My deck was too defensive for 3 damage to matter, and later in the game it's not big enough to attack past my opponents' creatures. Aviation Pioneer was also quite mediocre, but then I almost never needed Dwindle either since I had more removal than good creatures to kill. A couple of times the Pioneer's blue body turned on Gearsmith Guardian. Murder was really good as predicted, and even better with Salvager of Secrets (I got passed that late, too). Rise from the Graves also did quite well, including highlights of bringing back my opponent's Regal Bloodlord that made a bat, and a Leonin Warleader.
Yeah, Hired Blade is more of a filler creature; most of the time I like
Tolarian Scholar better. Flash is surprisingly irrelevant most of the time since you often don't have anything else to play anyway (sometimes you ambush a 1/3, but that's about what you can do really).
Pioneer giving you the 1/1 thopter as well as 2 blockers is mainly good against R/W aggro, but also against B/W if they go wide.
Salvager is good, but I found you can pick them up surprisingly late often. Not all blue decks want them and even those that do (mostly UB and UR) don't want more than 1-2 copies of it since it can be quite clunky.