Bills fan, but not here to troll. First, I don't think you can look at Allen and say, "it can happen to Tua too!" because what Allen has done from a development perspective simply hasn't been done by any QB that we've seen before. He's the exception, not the norm.
Second, Suggesting Allen was garbage in his first year in order to try and justify Tua's performances isn't a good look, nor is it really accurate. The idea that Tua's numbers are "much better" than Allen's is a really tough sell to anyone who bothers to actually look those numbers up. It sounds nice, but like claims of election fraud, fall apart when you actually look at the evidence.
PASSING
Allen 2018
12 GP
320 ATT
169 COMP
52.8%
2074 YDS
10 TD
Tua 2020
10 GP
290 ATT
186 COMP
64.1%
1814 YDS
11 TD
RUSHING
Allen 2018
631 YDS
8 TD
Tua 2020
109 YDS
3 TD
Purely passing, It's really hard to say that Tua was "much better" than Allen. More accurate? Yes. But I wouldn't look at either of those guy's numbers and be very impressed. Allen was 172 yds/gm, Tua 181.
However this is 2021, and running can be a big part of a QBs game. Allen blew Tua out of the water in this regard. Allen ran for 631 yds and 8 TDs to Tua's 109 and 3 TDs. So while if you put a gun to my head, I'd agree with the claim that Tua was a better (but not MUCH better) passer their rookie years, Allen was simply a much more EFFECTIVE QB overall. He contributed to the team at a higher rate than Tua with the time they each had on the field. He was able to make up for his accuracy issues and terrible WR corps (best WR was Zay Jones 642 yds.) by making plays other ways, to some extent. So that when you look at total offensive contribution, Allen's numbers are 2705 total yards and 18 total TDs to Tua's 1,923 total yards and 14 TDs.
Now I have no idea if Tua will turn into a franchise QB or not. But the problem I think you have is that his arm isn't really that special, and he lacks the athleticism and instincts to make things happen without his arm (or keep plays alive like Allen or Murray). He strikes me as a very cerebral, pinpoint passer. He's not going to be able to do things no one else can. The best Qbs today, Rogers, Mahomes, Allen, Lamar, hell, even Murray, you can look at their skillset and their tape and see that they can make throws and do things that maybe only 1 or 2 other guys in the league can. I think you have to hope he turns into a Brees who is able to knock a fly off a horses's *** from 50 yards away with his accuracy, because what else does he really do that well?? Is there anything in Tua's game that you can say that about? He's moderately accurate (65% is fine, but not great), and that's probably the best thing you can say about him. At least when you looked at Allen rookie year you could say, well, his accuracy is bad, but he has a cannon and is one of the top 2 or 3 running Qbs in the league that can literally hurdle a linebacker (see Vikings game)