There is no argument against - when you are learning to fly a kite for the first time, a trainer not being hooked to you is MUCH SAFER than being connected to a kite as you suggest the OP do before they have even flown a kite. And 2 hours on a trainer without lessons is no where near enough. I would recommend at least 10-12hours and at least 6 sessions ending only when you can tie a shoe with one hand while flying the trainer above you. You have to realize that the OP is brand new to a kite AND the wind. Can you tell him what too much wind feels like at his location??? Or would you recommend he buy a wind meter. And read up on "rotor". And read up on frontal gusts. And read up on cloud burst induced down/updrafts.
You are correct. But OP would have a huge initial investment with a 4m depower kite and bar. And the OP would likely not use that 4m for years on the water. I started off with 13.5 and a 11.5m years ago, even though I had lots of experience in high winds on depower snowkite foils at 3.0m (no fun though). I went down to 9.5m the second year, then 7.5 the third, then 5.5m a few years later. I only just went out with some confidence on a 3.5m depower (on water) last fall. It is pretty rare that any kiter lives in a location where you would even use a 4m at a high level of skill.
Instructors, some great ones I know, do teach right out of the gate with a depower kite. But they are there to explain what is happening and what the student is doing wrong. That is crucial, as the OP won't even understand backstall or line trim at the beginning. If anyone goes at it alone, I recommend they avoid moving right onto a depower at almost any cost. This keeps them many orders of magnitude safer with a trainer while trying to just figure out the basics of kite control and pull.
Maybe you have never taught someone to kite on a trainer, but the hardest thing to get through to students is to "let go of the bar". And that is extremely valuable practice that a trainer instills in a student. Trainers are the best tool to eliminate the powerful instinct that students have to "hold onto the bar for dear life", even when they are being dragged into a dangerous area or object. Again, no question that activating a safety is important. But you MUST let go of the bar first (which actually activates the safety on a trainer). Trainers teach this counter intuitive action better, and with little (damage to kite or person) consequence as opposed to the consequences a larger inflatable will have.
Bottom line is that trainers are safer, significantly less expensive, and more useful for at least 2-6 more years for the OP than your suggestion.