Ravi,
Don't believe for a moment that EVERY CFI out there knows more about aviation stuff than you do. I've met some pretty clueless ones my own self.
As to the 170, I always crack up when I hear that line about it being a "trickier airplane than you'd think". Great way to sell flight instruction, I reckon.
When I arrived here in CKN, a local spray pilot and CFI saw my airplane, and commented to the effect that I must really be a good tailwheel guy to land in a 170 in a wind (and it wasn't much). I looked at him sort of blankly, till I realized he was serious, then the light came on. I asked him how many 170's he'd flown? One.
Here's the key, and it has NOTHING to do with the tail:
You have to align the landing gear on ALL the Cessna Taildraggers. For some reason, 170's seem to receive this favor less frequently than the other models and seem to need it more.
Now, the original 120/140 had some landing issues, and some bright eyes fixed that with gear extenders, but there's no issues I've ever found with a 170 landing characteristics IF the gear is aligned right.
I've also flown some 170's that would do some really hinky stuff, BECAUSE the gear was out of whack, NOT because of a round tail.
As to wheel landings at 100 mph, all that does is risk your airplane and wear out wheel bearings. THAT, in my opinion, is NOT something I'd be doing and calling "training". How in the hey could rolling on the runway at 100 mph demonstrate that the round tail isn't BIG enough?
Sorry, rant over. That guy may have all the experience in the world, but if he's teaching what you descibe, I wouldn't fly with him.
I once went to Texas to do some aerobatics. Flew with a 19 year old CFI in a Pitts S-2C. Kid was simply one of the best CFI's I've ever flown with. Brave, but not stupid, no tricks, no BS, and no big ego. Great stick and a great instructor.
On day three of our flying, he told me he had a real treat for me: He'd arranged for a really well known local aerobatic instructor to fly in his place with me in the afternoon. Fine.
This guy gave new meaning to the word "brief" in the term "pre-brief". We got in the airplane, and he started trying to get me to do things I thought were pretty stupid, and made no sense, let alone didn't accomplish anything. He gave me grief, was rude and yelling, etc.
After 15 minutes, I announced the flight was over, landed and got out of the plane. The "old pro" asked me what the problem was. I told him that 19 year old kid in there was five times the flight instructor he would ever be, and that I would not PERMIT a student of mine to be subjected to the BS he was handing out.
The 19 year old asked me the same question, and I responded the same way. He was appalled, but he admitted that the old guy did do some kinda hot-doggy kinda stuff that really wasn't legal or smart, "but he's been around forever".
Next day, the old guy came up to me, unsolicited, and apologized, and complimented me on being willing to tell him my thoughts on the matter.
Get the dang gear aligned on the 170, and just learn to fly it. There aren't any "tricks".
Hammerhead turns in canyons are great ways to die in an airplane, if you ever really NEEDED to turn around in a canyon, in my opinion.
But, we all know what those are worth-opinions, that is

.
MTV