Good comparison in terms of draft position and age. But they're extremely different players, despite having similar natural assets. Wellingham is an explosive midfielder who plays outside and inside; Garlett is an explosive crumber.
I was watching the third quarter of the grand final replay again the other day, and I really noticed Wellingham's influence in the packs and around the stoppages. Of course, one quarter a tiny sample size, but it's the only footy I've seen for a while. People severely underrate his ability to win contested footy and get the hard ball. He throws himself at the contest, and has immense strength for someone his size [either that or he's slippery], as he can always be seen shrugging tackles in a congested area and making space to run into. His outside game is quite good too, though at times his kicking lacks polish. I think that he plays the inside role better, but Swan/Pendlebury/Ball generally fulfill that role the most.
The best comparison I can think of for Wellingham is Chris Judd in his West Coast days. At Carlton, he plays exclusively inside, but at West Coast he could play both. Wellingham obviously isn't anywhere near the level Judd was, but it's a stylistic comparison. He doesn't accumulate huge numbers, he generally doesn't get involved in the 1-2-3-4 handball chains. His touches come in and around stoppages, which is why he has a large influence on our success or failure in any given week.
Anyway, I went way off track... just thinking out loud about that discussion on Wellingham's 'inside' ability. I think Wellingham is and always will be the better player, but I do rate Garlett. Extremely talented and a valuable asset to have in any forward line. Perhaps could be better with a gun forward to crumb off. Both great rookie selections, that's for sure.