The "kickass Hansas" are in my experience harder to plan for as not only do you want/need rivers the same way and Oppidum wants/needs quarries and strategics, but planning a double or even triple dipping Hansa cluster means some rather difficult aqueduct and dam considerations (and you're limited to one dam per flood zone) that compete with river-adjacent commercial hubs. And the cities need more land both individually and overall to accomplish the central cluster while Oppidums can stand alone and only need a single 2nd ring tile.
I didn't find this to be the case personally.
Yes I might have to skip the odd aqueduct (dam placements are too RNG), but as long as the comm hubs are set up properly, you're still getting pretty decent hansas, and any aqueduct is really just icing on the cake for an already strong setup.
All it takes is really just three cities in a triangle, and if necessary I'll even sacrifice the river (which would fuel comm hub adjacencies and aqueducts).
Heck, I've even built the clusters from two cities, and while weaker, it's rather easy to set up.
The real benefit of Germany is that the extra district slot fits so well together in the overall picture.
Once you get the Hansa up, you essentially are allowed to place a "free" comm hub as well (a district you usually want anyway), which lends itself some extra production/food/(+ extra gold, science, culture, faith, if you have an alliance) to help get the rest up faster as well.
An early Oppidum (even when strong) forces you to make a consideration of whether the production is worth it over a different district, and that's the part I dont like for Gaul.
I havent really tried Gauls, but from my experience it is the case that (latent) early production is better than late (latent) production; I have frequently played Work Ethics and DotA to experience its benefit.
I believe that Oppidum is an adequate substitute for Work Ethics Lavras/Holy Sites if the right conditions are met (also, a reminder that Oppidum immediately gives +1P to mines).
Absolutely, but personally I consider Work Ethic stronger if we're considering "production now".
Along that extra production, you also get a lot of faith, which ties in nicely with a long-term investment plan (faith buying settlers, naturalists, rock bands, units from GMC etc.).
With Oppidum you only get "production now", and you have to hold out on any spill-over effects (since you just locked in a district slot).
(You can of course use that production to build monuments, granaries, builders etc., but I think those are less impactful in the grand scheme of things)