In the thread Do tones change at the end of an interrogative sentence? , one of the answers asserts:
SCALE KEY: 1 (low) to 5 (high). So 55 is a high level tone, 51 is a falling tone, 35 is rising, etc.
The second tone (textbook 25 or 35) often comes out sounding mid-level (33) or dipping-rising (434) -- this seems to be especially common at the end of a sentence.
Is this observation valid/true? If so, why does textbook-Mandarin teach that 2nd tone is 35?
XXX很难！XXX is so hard!
Here I understand 很 can be pronounced in a more drawn out/long way so as to stress the severity of hard.
你叫什么名字？What's your name?
Common phrase but 什么 (when spoken fast) sounds a bit like 33 to me.
我想去葡萄牙。I want to go to Portugal.
Pu2tao2ya2 also might be a good example of not completely saying 35 35 35 2nd tones.
I'm very interested in the ability of natives to, on the one hand, abide by the rules of lexical tones in daily speech, while on the other hand, modify/alter tones for the sake of convenience, pace, brevity, emotion etc. So when I stumbled upon this answer stating that 2nd tone isn't really pronounced 35 and instead is 33 / 434, I immediately wondered if it had any merit.
For sake of context, the same answer also included an observation on 1st tone's 55 modification in daily speech:
The first tone (textbook 55) is always level, but how high it is depends on the level of emphasis. It will be exceptionally high if you want to stress the word: 你喜不喜欢吃..中..餐 "Do you like Chinese food". It will often sound quite low as the second syllable in a two-syllable word (亚洲 "Asia" ya51 zhou22) and in other contexts where it doesn't need emphasis.