I get where you're coming from - on the other hand :
1 - there are few individuals capable of doing these things
2 - their time is their own (being so powerful, it is very hard to constrain them to a higher authority)
3 - dispel magic is a spell that exists
4 - making yourself reliant upon a fairly fragile system for essential processes is... bad
5 - for PC groups, doing the impossible is an everyday occurrence since the inception of the game
6 - "natural" obstacles of the kind you are talking about are not meant to be significant to characters of all levels
7 - you are assuming a good deal of time where there is no need for any kind of stealth or precautions (often in areas where such would probably be a good idea)
If you must, take the real world as an example of breaking points in such situations as you mention :
helicopters exist, they are fairly affordable (surprisingly so, I've found), there are daily traffic jams that cost over an hour a day to many, many, many people - I'm not seeing a whole lot of helicopter commuters...
I know it's not the best example - but I found it fun to write!![]()
It's all about resource cost - helicopters have a big cost-benefit ratio. So for rituals with shorter durations, I think your point is valid. But for longer duration spells, the ratio of benefit is tremendous compared to cost. Perhaps limiting ritual spell durations to 10% normal durations would solve the problem.