Is collagen supplementation useless?
Regarding the use of collagen supplements to help prevent or treat a tendinopathy:
A rather inconclusive quote from a 2016  systematic review {1}:

glucosamine and chondroitin sulphate, vitamin C, hydrolazed type 1 collagen, arginine alpha-keto-glutarate, bromelain, curcumin, boswellic acid, and methil-sulfonil-methane were considered […]. preclinical results are very encouraging, however they are not fully confirmed by clinical studies. There are few clinical papers on the use of nutraceuticals in tendon disorders, and their methodological quality is poor. Furthermore, in most of the studies more than one supplement was administered at the same time. This may bias the results, and the effect of each single component cannot be determined. Furthermore, the interactions between nutraceuticals and drugs, or other dietary supplements (especially at high doses) has not been evaluated, neither their effects on chronic diseases. For these reasons, it is not possible to draw any definitive recommendations on the use of nutraceutical supplementation in tendinopathies.


References:

{1} Federico Fusini, Salvatore Bisicchia, Carlo Bottegoni, Antonio Gigante,3 Fabio Zanchini, and Alberto Busilacchi. Nutraceutical supplement in the management of tendinopathies: a systematic review. Muscles Ligaments Tendons J. 2016 Jan-Mar; 6(1): 48–57. Published online 2016 May 19. doi:  [10.11138/mltj/2016.6.1.048] PMCID: PMC4915461. PMID: 27331031. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4915461/