You CAN directly access the photos from Finder. More on that in a moment.
Apple Photos is good for it's intended audience... but you have to understand the point behind it.
1) Most people shoot JPEG photos... not RAW. Photos is optimized for working with JPEGs.
2) Most people suck at organizational skills... Photos actually excels at this.
3) Photos prevents you from losing your original data if you edit an image.
On point #1: I think most serious photographers shoot RAW and want better control over fine adjustments and this is NOT what Photos is intended for. Apple's software for that was a program called Aperture (which they no longer sell). Aperture was optimized for RAW workflow.
Today, probably the most popular app for dealing with RAW workflow is Adobe's Lightroom. But you can no longer "buy" a copy of Lightroom, you now have to "rent" it by the month (and they require minimum 1 year periods.) They do include Photoshop with the rental of Lightroom ... for $10/month you get to use both (but that's $120/year).
On point #2: Apple noticed that people using typical software just import their photos onto the computer and they're just randomly dumped into a single directory. This makes finding a SPECIFIC photo rather difficult and also makes finding photos that are related to each other exceptionally difficult.
This is THE reason why Photos works the way it does (to save you from your own lack of organizational skills).
Photos maintains a library organized by year, month, day, and then the photos taken on that day. They do this because photos taken on the same day are possibly from the same event and therefore related. In the photos app you can certainly create albums, smart albums, or just use the imports to create automatic "events" (photos shot roughly at the same time).
However... seeing images in your Photos app is very similar to seeing them Finder in that you can just "drag" any images to your desktop... or anywhere else you want. So it's not a big deal.
On point #3: Photos maintains your original images (which it calls "Masters") so you can edit the images as much as you want. If you do an edit you later decide you don't like, you can always "revert to original".
You can find your original images in Finder by right-clicking the "Photos Library" and select "Show Package Contents". From there go into the "Masters" folder, then you'll find an entire sub-folder hierarchy based on year, month, and day in which the photos were shot.
Photos is MOSTLY written for the masses... casual shooters taken snapshots for family events and memories... not those who have a passion for photography. If you fall into it's target audience, it's great (it was the first program I know of to support facial recognition so if you want to see all the photos of you have of a particular person, it's actually pretty good at searching your entire library and finding them all and while it'll get a few wrong, it will mostly get it right (and you can correct it when it makes a mistake... the more you do, the better it is.)
For those who are passionate about photography, shoot RAW, etc. then I suggest using something optimized for RAW (Photos doesn't really support RAW... if you shoot a RAW it will immediately convert it to a JPEG and all adjustments are applied to the JPEG). You'd probably be happier with something like Adobe's Lightroom.
But a warning about many RAW editors... they do not save your finished work. What they really save is the original (Master) and then the list of every "adjustment" you applied to your image. When you open he image in Lightroom, it opens the master and rapidly re-applies the adjustments to construct your finished image. This means you can't just drag a file from Lightroom to SmugMug using Finder. However you CAN often find a "plug-in" for Lightroom. I think there is a SmugMug Plug-in for Lightroom (to allow direct uploads to your account via Lightroom). I don't use SmugMug so I cannot vouch for how it works.