Please Note: I receive no endorsement to promote or discuss these pens and all thoughts contained within here are my own at all times, and there's no influence through out the post, I own both of these pens and have USED them extensively.
Let's talk money, the Ystudio will run you $99.99, the lamy will run you 89.99(However there are some colors on sale depending on where you are looking).
The Ystudio uses a European refill standard refill, the one that is equipped in the pen is a Schmidt 888F, these are a fairly cheap refill that can be found on Amazon for $10.99 for 3, where the Lamy runs a M66 lamy refill that's a M or F depending on your region (Australia get a M and B)and supplier and these will run you 12.99 and can be purchased in black, blue, green or red.
The Lamy Swift has been the pen that I have rocked to work for a constant 4 or 5 months until I found a cheaper pen that I liked and didn't need to risk losing or breaking. The Swift has lived in my planner for a while as well as a pen for using with my planner but I have ended up replacing it with a Kaweco Special as I prefer a fountain pen.
The Ystudio has four colors Dawn Yellow, Sky Blue, Evening Purple & sea Indigo (Sunset Orange didn't drop in Australia Telegram Co, I excepted better). The Lamy Swift has Blue, Black and Palladium - Limited Editions have included Neon Orange, Black Forest, Racing Green, White and Graphite - Neon Orange & Graphite are still floating around in certain stores.
The downside of the Lamy is it's the one pen you'll either love or hate and if you love it you got to catch em' all. I think that's what happens when you love a good pen, or maybe I am confusing that with Pokémon lol. I think the M66 refill is more easily sourced at somewhere like your local Officeworks, when the Euro Standard would be more specialist and requires google or milligram or bookbinder design.
I think that the Lamy looks more business class and more professional where you'd find lawyers and office people using that pen, where the Ystudio is more fun and playful and you'd find that one floating around University's students and tech startups, I think the Ystudio would be right at home with UP bank and tech company's and Finacial companies like that where the Swift expresses a more professional approach.
Ink is one of the one of the biggest things when it comes to pens and that's just a fact of life. The Schmidt 888 F (0.6 is considered fine, however this is a 0.9 according to specs) isn't my favorite ink cartridge to write with and that is a vital part, of what makes a great pen though the refill is somewhat inexpensive though, so that's a bonus unlike the M66 refills however over time and the more I write with the Ocean, the more I have come to love the ocean rollerball, but I feel like there's a few strong points to each pen. Schmidt 888 thickness is on par with the Lamy Medium M66.
I think the rounded pen shape for the swift is better for most people and will work better in larger hands for most people for the most part. I think the Swift is going to be an easier find at a more competitive price compared to the Ystudio as Milligram (Telegram Co) in Australia has the market cornered for that.
The Ystudio brand is very much a cult classic in Australia and that makes it a struggle for people to source cheaply where the Lamy swift there's a few additional retailers that can focus on keeping the costs of the pen down a lot which makes the costing more competitive, and it might be a better budget option.
Conclusion: Based on the recent movement of the Ystudio Ocean to outlet with Milligram, the Australia Distributor's it becomes a fast pen that is easier to recommend over the Swift, because the swift will be here for years to come as it's keystone of the Lamy elegant rollerball range where the ocean once gone we won't be seeing that back again and that truly sucks to be honest as I love the ocean.