No I don't see anything wrong with it. I have software that offer a choice between a free version, with a limited set of features and/or restrictions on other features, and a full price version with the full range of features and no restrictions. Some products have price tiers - a free version , a basic price version (with more features and fewer restrictions) and a full price version (with everything).
Just because DTG does or does not do something is no reason for N3V to copy them.
Of course you don't see anything wrong with it. I'm not surprised. There are a lot of people who are more than happy to say "Shut up and take my money" to an obviously problematic business practice that can easily do more harm than good.
N3V Wouldn't be copying them. TSC didn't even have any subscription to begin with, so it's possible DTG took a page from N3V's book just to rake in extra cash as if they don't already make enough from TSW and TSC.
DTG at least do a much better job with the rail subscription. All the dlc in the rail subscription can still be individually purchased. That's a good thing, that should be the norm. Trainz shouldn't be any different. N3V will end up diving the community if they keep making dlc exclusive to Trainz Plus. They shouldn't be doing that at all. N3V Games may be a small team, but they're still held to the same standards as any other developers and publishers. You don't just lock dlc behind a subscription when a majority of dlc is still purchasable. That's shady and rightfully rubs people the wrong way. That's how you divide your player base. A tiered community isn't a good look, nor is it a good thing to do. If anything, it pushes people away. The subscription is fine, however making some dlc exclusive to Trainz Plus is not.
I don't care how many benefits the subscription comes with. What's wrong is wrong. It's favoritism. The HST, the Superliner Pack, those dlcs have been exclusives for years and yet, still aren't purchasable. N3V Games could have just added all the Trainz Plus exclusive dlc as bonus content for Trainz 22 Platinum Edition, but they didn't. Instead they chose to keep certain dlc locked behind Trainz Plus, to make extra money, at the cost of pissing off Trainz users, especially me. That's a shady business practice and I consider it a red flag. All dlc should be purchasable. Snowrunner, Mudrunner, The Sims 4, Train Sim World, dlc can be purchased for those games. They're not locked behind gamepass. Trainz shouldn't be any different.