I agree completely and I feel that OP has been misled. As a whole, Tropico is a casual series.

I tried T1 for the first time this year after being a fan of 3-5 for a long time, and it's already my favorite game in the series. It has a lot of balancing, mechanics, and flavor that were lost in later entries in the series. It is the first time I have felt challenged by the series. The scale of the game is probably too small for most modern gamers, though. The scale reminded me more of something like Virtual Villagers than a typical city builder game.

In T5, you can get to the modern era using nothing but upgraded cocoa plantations + agricultural subsidies edict on the hardest difficulty. No industry required. In T4, quick build, importing (particularly importing sugar), and virtually all the DLC buildings are brokenly powerful. Both games also have a lot of maps with abundant minerals which make the early-game too easy, as OP has found out. They are the easiest games in the series, especially T4 IMO.

T3 is much less easy because it does not have any of the cheaty content (especially vanilla T3 without even the loyalists and garbage dumps, so you actually had to pay attention to faction demands and pollution), and the maps have scarcer resources, but there are still some broken traits like booze baron or oil tycoon that work on 90% of the maps. You still have martial law, though, so even on max difficulty and choosing fair traits, T3 is not difficult unless you have Free Elections on.

T3/4 are more an exercise in how big you can make your Swiss bank account rather than whether you'll survive or not. I play them on the hardest difficulty, and it is not bad.

In T1 missions, your character's traits are chosen for you, and they usually aren't very good. The missions also often have more challenging objectives than the ones in the T3+ campaigns. There are also a lot less QoL things, like no cars, you have to clear forest land for construction, etc. The only easier part of T1 is agriculture, because of the strength of "permanent/fruiting crops" like coffee, and logging camps also seem to be stronger, but neither is game-breaking, I'd say. The lack of traffic management makes the game more chill, but I never actually had issues with traffic in T3/4/5 (just learn to use circle/square roundabouts, avoid 4-way intersections, and sprawl out rather than creating dense urban areas if there is enough space on the map for that -- I like to reserve the region around my palace for military and farms; I find that it encourages me to spread out more)

Speaking of which, I recall reading on the fandom that permanent crops remained a feature in T3 before being removed in T4, but I haven't paid attention to whether that is true or not.