Throwing out the finite nature of online, a better reward for max rank would have been one of the more flashy and unique vehicles like this big boy. Not only is it a jet powered big rig, but is allegedly faster than the other rigs in the game by a slight margin. Not sure if that's true or false, but the griefers seemed to think so, seeing as this was their go-to vehicle.
For the Deerstalker itself, I would have tossed it in as a career unlock like most of the game's content.
Personally, as a outsider looking in, I don't think any reward could justify the difficulty it takes to get to the top just based on what you said. Having things that can only be unlocked online is generally a bad idea in my opinion because not everyone is able to participate in it and those servers aren't going to last forever, which means some people will miss out on them. Though I suppose their has to be something to encourage players to play online more.
I can remember playing Tiger Woods PGA Tour 2005 a long time ago and it had some things that could only be unlocked online. It bummed me as a kid because I had no means of playing online and therefore could not get them. It's even worse now because I can't imagine the servers being active anymore due to how old the game is.
Need for Speed Carbon is another example of this as well. I tend to forget about this, but it has some reward cards that can only be obtained via online and it's a shame because some of them are genuinely good. The Porsche 911 GT3 RS might just be the most offensive of them all because it requires you to reach Online XP Level 50 and to beat an EA moderator in a ranked online game. I don't know much about online play in Carbon because my time was spent mostly on the PS2 version, but I can't imagine that being easy and what's the likelihood you'll ever encounter an EA moderator anyways?
It's a pity because it's a nice car! Fortunately, from what I gather, the servers might still be up.
I'd like to add the Nike One 2022 (holy 🤬 just one year to go), awarded from both the IB license and the Saleen S7 one-make, which is as pointless as it comes. As a general rule I don't enjoy winning the same car I already used in a one-make, but even getting another Saleen to make up for the costs of buying one would be more satisfying.
While I love the Nike One 2022, I do kind of wish they had put something else in it's place for IB License because having it in as a reward in two places seems kind of pointless. While I fail to see how it has any relation to Saleen whatsoever, I'm fine with it being there since I can win it again if I ever need to. The same can't be said for IB License though.
In fact, most of the early cars you win in any GT game are just instantly forgettable. In GT2 you win standard Clios, Yarises, MX-5s and MR-Ses. Complete trash that will be instantly sold.
GT4 is one that comes to mind for me. I can remember completing B License when I was 12 and being rather unimpressed by the Volkswagen Lupo it gave me. Small achievement means you get a small reward in return I guess? I never found a use for it, but I could be misjudging it though. The Autobianchi Abarth is one I felt similar towards as well, but it later proved to be useful and maybe the Lupo is the same way? Still, I can't say I am amused with the Lupo as a reward. Though I must confess, I haven't played GT4 in a very long time.
