I'm starting to remember why I stopped playing this game.

Yeah, that's pretty much what Gacha games are. You're gambling to get a CHANCE at what you want. That's basically every gacha game, it pretty much defeats the purpose of being a Gacha if you could just buy the unit that you want.

"Let me just buy 5* Donnel's so I can get 5* +10 Donnel way faster."

There's no sense of accomplishment, and that takes away from a lot of the fun. Being able to use your hard-earned resources to finally upgrade that unit you love to the best it can be.
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What you just described is what a lot of people feel during a lot of the banners in this game. The whole point is to summon units and make them stronger. That's basically it. If that's not your cup of tea, then perhaps this wasn't the game for you. While I do agree, I love Fire Emblem games, this game is not the same as, for example, Awakening, Fates, Sacred Stones, Binding Blade, or practically any other Fire Emblem game.

I play for the puzzles and the fun of seeing your favorite units comes second to me.

It is because fun is how you dictate it to be for yourself. Just like life is whatever you want to make it to be, this game is similar to that. If you want to just get by, for most part yea it is not a problem. If you want to have it very good, then you will need some luck and breaks here and there, but for most part, you will need money.

To some people, living in an affluent area, with nice, car, clothes, and everything else is living, to others they can be happy and fine with just the simple things.

Of course there are big differences in life and a game. However, some of the similarities is how you define your own enjoyment of it, and what you deem as necessary. For example, I am fine spending in this game, but I am not fine spending 100k on a car. Not that I cannot afford it, but it just doesnt appeal to it. The person who have no problem spending 100k on a car may look at spending in a game, or even playing one is a total waste of time and money.

It basically is what you make of it, literally. If your enjoyment is wanting to be at the top of this game in competition, then yes, it will be much more difficult as a F2P player.

At the end of the day, money makes a lot of things easier, but you are the one that has to define what is proper for yourself on entertainment and value.

My advice on people who wants to spend very little or not much at all is to avoid niche heroes and pursue heroes that are force multipliers and can do a lot of things well. This way you can use them for just about anything and do so well. Niche heroes may be super dominant in an area or two, but easily affected by changes in game and shift of balance.

If you are going to spend, Id recommend putting this spending as part of your entertainment budget as a whole so you dont go overboard with it beyond what you are ok with. If you are having concerns with it, then it is usually a sign of slowing down or just stop spending.

The game is fun, even if you don't get each hero of a new banner.
Like someone already said : if you want to play this game for free, try to focus on all-rounder heroes, that are pretty good in total and basically any team, if you want to play special heroes, you can even get them after a while.
Nintendo gives away lots of orbs for free during these days.
I myself spend about 60 Euro on this game (because i thought, that this is the amount of money i would be willing to pay, according to the fun i have) and at this point, i own about 45 5* heroes, including the ones i upgraded with feathers, but still a decent list.
Just play whenever you feel like it, enjoy playing with your favourite heroes and don't try to get everything and everyone, since that's impossible without paying money all the time.
If you want to play fire emblem without this random factor etc. i strongly recommend playing the normal games on console or handheld, they are really nice and include way more tactics and options than FE Heroes.

Of course the main focus of the game is to summon, I didn't go into this expecting a grandiose adventure/story, nor a traditional fire emblem game. It's to collect your favorite/strong characters and have them fight alongside other characters from other worlds. No offence, but you kinda went into this with the wrong mindset for a fire emblem based gacha game. Of course they wanna get money, if most/everyone was F2P then they wouldn't make too much profit and the game wouldn't be as successful as it is today, and even then they do so much in terms of free stuff compared to other gacha games. Still, if it bothers you a lot, I would recommend dropping the game, because it definitely won't change.

Honestly, the real fun comes in trying to make it to Tier 20 with what you have, and building up your units. Like right now, I don't care about summoning at all because I want to save orbs and am not enticed by the banners. Right now, I need feathers more than anything. That requires a lot of grinding, which can take the fun away too.

Arena is really fun, especially trying out gimmick builds and such.

Honestly, summoning is fun, but since February 2017 I am at a point where I have 72 different 5 stars and almost 100k feathers saved for later, spending about $120. I don't need to summon,I just want to sometimes. I skip banners until I have 100-200 orbs saved up, and only really pull for specific units that fit what I want. I skipped Miciah's banner, went for Myrrh and Legendary and got lucky, sometimes I am not. I no longer have the urge to spend real money.

I find fun in this game at home, school bus, car, etc. Unlike big games like Persona 5 where it's best to play in large sittings, Heroes is easy to pick up whenever. I'm not saying I don't like huge games that may be cheaper than these gachas, it just fits my lifestyle. I love a variety of games.

My only complaints are not being able to challenge friends in casual PvP. It was mentioned in the survey, so it may be added.

How many heroes do you have? Honestly you only need 35 good ones to get by, but pity breakers can be a pain. I understand where you are coming from, but getting access to all these heroes would take away the need to do anything. You and your opponents would all run Kitty Paddles, Breaths, DC, CC, etc. on everyone. You don't need to be overpowered to win. Easy units like Nino are available, free brave units, Fjorm, Tempest units...

Hope this answers your question :)

A lot of good answers here.
Honestly it does come down to how you want to play this game. When I first started I invested a lot of time into it like I would any console game but now I play it a lot more casually, when I’m on my breaks at work or I’ve got a bit of time, I enjoy the GHBs, BHBs and arena battles for the challenge and strategy. But this equates to maybe 30minutes to an hour a day. I mostly play my other games, at the moment I play a lot on my switch.
Up to you how you invest your time into this game.