Well, if your position is not only that the DM will enable (for example) planar travel to the planes he has determined the plot will take the players to, but also that he will actively forbid spells that would allow them to get to planes he didn't specifically plan for non-spell ways to get to them, then yes, the caster abilities that enable the thing he DM will ensure do not work don't matter.

However, if the players tell the DM, "We would like to go the Plane of Fire," he may ask "why" but he also almost certainly will ask "how." And if the players say they are going to do research into planar portals, the DM decides whether they can find anything at all, and also where the portals are on both ends and how they are activated.

Sure, he can do a lot of the same if the players' answer is, "Wizmadoo will cast plane shift to get there," because he can make some of thise hoops they must jump through be to get the tuning fork. However, once Wizmadoo has the fork, he can cast the spell every day. Moreover, with a portal, Wizmadoo and party can get cut off from that portal, and have to find their way back, fighting or sneaking or whatever. If the party is stuck on the Plane if Fire with Wizmadoo, he can just cast the spell to go back home at any point he has a spell slot of the appropriate level available.

The DM's freedom to put them anywhere on the plane he likes is like the ability to set the portal location, but even that is unlikely to go to the same (undesirable) place every time. (A teleportation circle to target is a choice on the players' part whether to use or not, especially if they can create their own!)

These spells just put much more in the hands of the players, giving them more agency. Unless the DM essentially bans them.